Traditionally, the cast is given clues to guess the identity of the episode's guests, and once the guests appear and are introduced, they and the cast are given a set of puzzles to solve.
Unexpected Business
Wait Wait... Don't Tell Me!
Problem Child in House
22/7 Kenzanchu
LIGHTHOUSE
BAZOOKA!!!
Le Grand Échiquier
Who Wants to Be a Millionaire?
8 Out of 10 Cats
The Kelly Clarkson Show
StarTalk with Neil deGrasse Tyson
The Tonight Show Starring Johnny Carson
The Dick Cavett Show
Game-Lu?Game-Lu!
Off Gun Fun Night
The Night of Hate Comments
Where on Earth Is Carmen Sandiego?
The Wiggles
Scooby-Doo! Mystery Incorporated
Numberblocks