The free spins feature in Loki's Riches is triggered by landing 4 or more scatter symbols (represented by a book), awarding 10 free spins. During the free spins round, a random pay symbol is selected to be the special expanding symbol, enhancing the chances of forming larger winning clusters. Additionally, landing 4 or more scatter symbols during the free spins round will retrigger an additional 10 free spins, providing players with an extended opportunity to maximize their winnings. This feature is significant as it not only offers free chances to win but also increases the potential for bigger payouts due to the expanding symbol mechanic.