Guess Who?

(Hasbro’s) Guess Who? is a “search race” game between two players. Each player selects a character from a pool of 24 cards. The objective is to be the first to find the opponent's character by asking in turn YES/NO questions about the (physical) attributes of the character.

The rational gameplay strategy is to ask a "halving" question. But if the opponent is ahead of us then we should ask a "riskier" question with a better best-case value.