During the free spins round, whenever the chosen symbol appears on a reel and can form a paying combination on an active line, it expands to fill the entire reel (all three positions). This is the mechanic that creates the game's explosive win potential.
Critical rule: Expanding symbols do not need to sit on adjacent reels to form a winning combination. They only need to occupy the correct reels for a payline. For example, if Rich Wilde is the expanding symbol and appears on reels 1, 3, and 5, the game evaluates whether those positions satisfy any active line and pays accordingly.
Landing three or more Book symbols during free spins adds another 10 spins with the same special expanding symbol. There is no published hard cap on retriggers, though chaining them is rare.
The randomly chosen symbol is destiny, frankly. If Rich Wilde (the top-paying symbol at 5,000 coins for five) is selected and appears on multiple reels, the round can produce payouts that dwarf an entire base-game session. However, a low-paying card symbol selected as the expanding symbol typically yields modest returns. This randomness is the core of the game's high variance.
From long-term observation, two patterns hold: mid-tier expanding symbols (Pharaoh, Anubis) often produce steadier returns than the top symbol because they land more frequently. And retriggers are deeply uneven. You can play hundreds of spins without seeing one, then chain two in a single feature. Plan around that variability.
The gamble feature is also worth mentioning here. After any winning spin in the base game, Book of Dead offers an optional risk round: guess the colour of the next card (red or black) to double your winnings, or guess the suit (hearts, diamonds, clubs, spades) to quadruple them. You can gamble multiple times in succession, but a wrong guess forfeits the entire win from that spin. It is not available during free spins and is strictly optional. Some UK-licensed platforms may restrict or disable the gamble feature as part of consumer protection measures.