The phrase "crawling on all fours" can be described in various ways, depending on the context. Some synonyms to describe the action can be, "grazing", "scrabbling", "scuttling", "scurrying", or "creeping". When used to depict a person's movement, "kneeling and crawling," or "slithering" can be used. When referring to an animal's movement, "prowling," "hunting," or "foraging" on all fours can be used. Depending on the tone of the sentence, the phrase can also be given a more playful vibe by saying "prancing" or "galloping" on all fours. Whatever the synonym used, it is important to ensure that the context and message are accurately conveyed.