Expanding Symbols Deep Dive - How ‘Book of’ Slots Really Work

One symbol picked at random before free spins expands to fill whole reels and pays even across reels that are not next to each other. We break down the ‘Book of’ expanding symbol through one bonus round, its family tree, a field guide to variants and its effect on volatility, based on the games’ own rules.

AI Slot Editorial TeamAI Slot Magazine

Published2026.11.08

Reading time16 min

There are dozens of slots called ‘Book of’, but most of them run on the same engine. Three book symbols open free spins, one symbol is drawn before the round, and that symbol stretches over whole reels and pays even across reels that are not next to each other. The device is called the expanding symbol.

Unlike our other deep dives, this one is laid out as an anatomy chart. We first take apart one bonus round of John Hunter and the Book of Tut, then trace the lineage and the variants, and finish with volatility and a demo checklist. Feature descriptions follow the rules text inside each game’s official demo. For an overview of the genre, see the Book of slots wiki entry.

Anatomy - One Bonus Round of John Hunter and the Book of Tut

John Hunter and the Book of Tut is a 5-reel, 3-row payline slot released by Pragmatic Play in May 2020, with an RTP of 96.50% according to AI Slot data, and its official demo start screen shows a max win of 5,500x and medium volatility. Following the order written in the game rules, one bonus round goes like this.

1. Three scatters: three or more book symbols, which act as wild and scatter, anywhere on the reels start the free spins feature. Three, four and five books also pay 2x, 20x and 200x the total bet.
2. Symbol pick: before the round starts, one special expanding symbol is chosen at random. It stays the same until the free spins end.
3. Free spins: 10 are awarded. Three or more books during the round add 10 more with the same special symbol, with no limit on retriggers.
4. Expansion: on each spin, regular wins are paid first, then the special symbol expands vertically to cover all 3 positions of its reel. Expansion only happens when enough special symbols land for a win.
5. Payout: the expanded special symbol pays by its own paytable, on all reels, even in non-adjacent positions. A spin’s win is therefore the sum of two payouts, the regular win and the expansion win.

Of the five steps, step 2 decides the most. Depending on what is drawn, the same 10 spins become a completely different bonus, which we return to in the volatility section.

How It Pays - Why Reels Far Apart Still Connect

On a normal payline slot, a win must run unbroken from reel 1. Matching symbols on reels 1, 3 and 5 do not pay if reel 2 is empty. The expanding symbol skips this rule. If the special symbol lands on reels 1, 3 and 5 and all three expand, every position on those reels holds the symbol, so any payline you draw crosses it three times. The game counts that as a three-of-a-kind on each line.

So an expansion win comes close to ‘one line win times the number of paylines’. The more lines a game has, the bigger the hit when it expands. Play’n GO’s official description of Book of Dead explains the same principle: the expanding symbol only expands when it creates additional wins on active paylines, and the expanded symbols do not need to be next to each other.

The Book - Wild and Scatter in One

The ‘book’ that gives the series its name usually plays two roles at once. The John Hunter and the Book of Tut rules say this symbol is both scatter and wild and substitutes for all symbols, and five books pay by the wild paytable. Play’n GO’s official Book of Dead guide also describes a symbol that is both wild and scatter. Novomatic’s Book of Ra deluxe 6 product page likewise describes the book as a wild that substitutes for other symbols.

This double role comes at a price. As a wild the book links base game wins, but since the same symbol also holds the key to the bonus, studios have to keep it rare. So some newer games split the roles. Book of Tut Megaways states that its wild substitutes for all symbols except the scatter and keeps the scatter as a separate symbol, and Book of Kingdoms also separates the bonus symbol from the wild. Wilds in general are covered in our wild symbol deep dive, and pay-anywhere scatters in the scatter pays deep dive.

Family Tree - From Book of Ra to Pragmatic Play

The game usually named as the root of this design is Novomatic‘s Book of Ra. Novomatic’s official product page presents it as an Egyptian-themed 5-reel, 10-line video slot but does not give an original release year, so the table below leaves that year blank. The game that popularized the design online is Play’n GO‘s Book of Dead, released on 14 January 2016 according to the company. Pragmatic Play then reshaped the device in several directions, mostly through its John Hunter series.

Dates for Play’n GO and Greentube come from the companies’ official material, and dates for the Pragmatic family come from release dates in AI Slot game data.

Field Guide to Variants

The classic form is ‘one random symbol, fixed for the free spins, 3-position expansion, non-adjacent pays’. The rules of John Hunter and the Book of Tut and Book of Vikings use nearly the same wording for it. Each variant changes one of those four parts.

Two expanding symbols

This turns ‘one random symbol’ into two. Novomatic’s Book of Ra Two Symbols product page promotes more free games and double special expanding symbols, and says the Golden Book opens when the Extra Bet is chosen. Two candidates mean more chances to expand, and the studio balances that somewhere else.

Pick your own symbol

Here ‘random’ becomes ‘chosen’. The rules of John Hunter and the Book of the Fallen say that before the 10 free spins start, the player can select the special expanding symbol. There is also an ante option in the base game: paying 10x the total bet makes every spin play like a free spin, with the preselected symbol expanding and paying anywhere.

Expansions that grow as you collect

This changes the ‘3-position expansion’. Book of Golden Sands is a 6-reel ways game where one of all paying symbols is drawn as the special symbol before free spins. Expansion happens when at least 3 special symbols sit on different reels, and one instance of the symbol is collected on top of each expanded reel. Later in the same round, that reel expands to 3 plus the number collected, up to 10 positions. Pays follow the number of ways formed by expanded symbols on each reel, again even on non-adjacent positions.

Base game expansions

This extends ‘fixed for the free spins’ into the base game. Book of Tut Megaways has up to 7 symbols per reel and up to 117,649 ways, and on random base game spins one paying symbol is drawn as a special expanding symbol. After regular wins are paid, it fills every reel it is on only if the expansion produces at least a win. The Megaways engine itself is covered in our Megaways deep dive.

Gamble-to-upgrade

Book of Monsters plays on a 7×7 screen and uses a large ‘FAT symbol’ instead. A random paying symbol becomes the FAT symbol before free spins, and before the round you can gamble separately to raise the FAT symbol to the next higher-value one or to increase the number of free spins. If the book’s pages reveal the next step the gamble wins, and if ‘THE END’ appears it loses and the round ends.

How It Differs from an Expanding Wild

Both cover whole reels, but they do different jobs. An expanding wild substitutes for other symbols to complete lines, so wins still have to be adjacent from reel 1. An expanding symbol is itself the winning symbol and skips the adjacency rule. The Book-style expanding symbol also mostly works only in free spins. So expanding wilds tend toward ‘often and small’, and expanding symbols toward ‘rarely and big’.

Volatility: It All Comes Down to Which Symbol Is Drawn

In an expanding symbol game, the bonus is decided at the starting line. If a low card symbol is drawn, even five expanded reels pay little; if the top symbol is drawn, the same scene can approach the max win. A figure like the 5,500x max shown on the John Hunter and the Book of Tut demo screen mostly needs a top symbol pick, several expanded reels and retriggers to stack up. Even the classic form gets different ratings: Pragmatic marks John Hunter and the Book of Tut as medium volatility, while Play’n GO’s official guide calls Book of Dead a high-variance game.

The variants differ in how they handle this luck of the draw. Book of the Fallen turns it into a choice, Book of Monsters lets you bet on it again, and two expanding symbols split it. Growing expansions like Book of Golden Sands make each expansion worth more late in the round, widening the range of outcomes. The concept itself is in the volatility wiki entry.

Buys and Antes - Paying for the Expanding Symbol Up Front

Most Pragmatic-family Book games state in their rules that free spins can be bought instantly for 100x the total bet. Antes vary by game: Book of the Fallen charges 10x for an expansion every spin, Book of Tut Megaways uses a 25x bet multiplier to raise scatter chances, and Book of Monsters uses a 40x bet multiplier to lower the trigger from 4 bonus symbols to 3. In some games turning on the ante disables the buy. The history and regulation of buys are in our bonus buy deep dive.

Demo Checklist

When you first open a Book-style game in free demo mode, check these items one by one in the game rules (the i button).

• The book’s role: is it both wild and scatter, or are they separate?
• How it is picked: random or chosen, and how many?
• Expansion condition: does it need enough for a win, or 3 on different reels?
• Non-adjacent pays: do the rules say ‘non-adjacent’ or ‘pays anywhere’?
• Retriggers: how many spins are added, and is there a limit?
• Buy and ante cost and RTP: is a separate RTP listed for the buy?

Frequently Asked Questions

Do expanding symbols appear in the base game?

In the classic form it only works in free spins. Some games differ, such as Book of Tut Megaways with random base game expansions, or Book of the Fallen, where a 10x ante makes every spin expand.

Does the expanding symbol have to start on reel 1?

No. The rules of John Hunter and the Book of Tut and other Book games say the special expanding symbol pays on all reels, even in non-adjacent positions. All it needs is enough symbols for a win.

Are regular wins lost when the symbol expands?

No. By the rules, regular wins are paid first, then the expansion happens and its win is added separately.

Can the book itself be drawn as the expanding symbol?

In the rules we checked, the special symbol is chosen from the regular paying symbols. Book of Golden Sands says ‘out of all paying symbols’, and Book of Kingdoms says ‘from all symbols except BONUS and MONEY SYMBOL’.

Related Reading

Wild symbol deep dive · Scatter pays deep dive · Bonus buy deep dive · Megaways deep dive · Book of slots · Rich Wilde series · Reel Kingdom

Sources: Pragmatic Play official demo game rules (John Hunter and the Book of Tut, Book of Vikings, John Hunter and the Book of the Fallen, Book of Golden Sands, Book of Tut Megaways, Book of Monsters, Book of Kingdoms), Play’n GO official game page and guide (Book of Dead), Novomatic official product pages (Book of Ra, Book of Ra deluxe 6, Book of Ra Two Symbols), Greentube press release (Feb 2023), AI Slot game data