The phrase "prick up" means to suddenly become more attentive or interested. It is often used in the context of animals, such as when a dog pricks up its ears to listen. There are several synonyms for this phrase, including perk up, become more alert or attentive, become more interested, become more responsive, and become more attentive. All these expressions convey the concept of becoming more attuned to surroundings or paying more attention to what is happening. These synonyms can be used interchangeably depending on the context, but their meaning remains the same, indicating an increase in attention or responsiveness.