You can't lie.

　　Because if you can lie, when the undercover guesses the civilian word, you can describe it completely according to the civilian word. At this time, everyone on the field describes the same word, and the voting is completely random and intuitive, so there is no point in continuing. So undercover can't lie.

　　But if undercover can't lie, as long as the civilian description vocabulary is infinitely obvious, undercover can't win. Therefore, when the undercover guesses the civilian words, he can choose to blow himself up, and at this time, he should be sentenced to victory. The essence of the game is to establish the rule of self-destructive guessing, that is, to ensure that the description of civilians can not be too obvious (to prevent being guessed) and too vague (to be easily voted out).