The phrase "knew what makes tick" refers to understanding someone's motivations or interests. There are several synonyms for this phrase, including "knew their likes and dislikes," "understood their preferences," "grasped their motivations," "figured out their passions," and "cracked their code." These phrases are all used to describe the ability to understand someone on a deeper level, beyond surface interactions. Knowing what makes someone tick can help build stronger relationships and personal connections, allowing for better communication and understanding. It is important to take the time to understand those around us and their unique motivations and interests.