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Phrase(s): what makes someone tick
Fig. something that motivates someone; something that makes someone behave in a certain way. (Fig. on what makes something tick.) • William is sort of strange. I don’t know what makes him tick. • When you get to know people, you find out what makes them tick., Phrase(s): what makes something tick
Fig. the sense or mechanism that makes something run or function. (With reference to the ticking of a clock representing the functioning of the clock.) • I don’t know what makes it tick. • I took apart the radio to find out what made it tick.
McGrawhill's American Idioms And Phrasal Verbs