The phrase "knows what makes someone tick" refers to understanding someone's motivations and desires. Synonyms for this phrase include understanding someone's drives, passions, and instincts. Knowing someone's likes and dislikes, idiosyncrasies, and quirks are other ways of understanding what makes someone tick. Being able to predict someone's behavior, thoughts, and reactions can also be a sign that one knows what makes them tick. Understanding someone's personality and character are also important in knowing what drives them. Overall, understanding what makes someone tick is essential for building strong relationships, effective communication, and successful interactions.