The phrase "crawls all fours" can be replaced with a variety of synonyms to describe movement. Some options might include phrases such as "creeps on hands and knees," "scuttles low to the ground," or "slithers on their belly." Each of these phrases captures a slightly different sense of movement and might be used to convey a particular mood or feeling in a piece of writing. For example, "creeps on hands and knees" could suggest a sense of stealth or trepidation, while "slithers on their belly" might evoke a more sinister or menacing tone. Overall, there are many possible synonyms to choose from when describing the movement of an animal or person on all fours.