Simplify the following text for a Grade 3 native English-speaking person.
Original: For example , Gollum 's riddles are taken from old historical sources , while those of Bilbo come from modern nursery books . It is the form of the riddle game , familiar to both , which allows Gollum and Bilbo to engage each other , rather than the content of the riddles themselves .
Simplified: Gollum and Bilbo play a game of riddles .