brain teaser

 Longman Dictionary of Contemporary English 5++朗文当代英语 5++LDOCE 5++朗文 5++ˈbrain ˌteaser noun [countable]  SOLVE/DEAL WITH A PROBLEMa difficult problem that is fun trying to solve 有趣的难题，智力测验题

ˈbrain ˌteaser nounChineseSyllable  

brain teaser
ˈbrain ˌteaser noun [countable]
a difficult problem that is fun trying to solve