When it comes to recalling something quickly, people often use the phrase "making up the top of one's head." However, there are several synonyms that can be used to express the same idea. For instance, some other phrases that could be used instead are "off the cuff," "on the spot," or "from memory." Additionally, "pulling something out of thin air," "winging it," and "ad-libbing" could also be used to describe the act of quickly recalling information without prior preparation or thought. Ultimately, there are many different ways to describe the process of recalling something quickly, so it's important to choose a phrase that best fits the situation at hand.