The phrase "fall open" can be expressed using a variety of synonyms, such as swing open, flop open, unhinge, unclasp, and unbolt. The term "swing open" implies a smooth and easy motion, while "flop open" suggests a more sudden and abrupt movement. "Unhinge" can be used to describe a door coming off its hinges, while "unclasp" and "unbolt" suggest removing the clasps or bolts that keep a door closed. Other synonyms for "fall open" include "burst open," "fling open," and "fly open," each with their own subtle connotations. Whatever synonym is used, they all describe a door or container opening with a certain degree of force or motion.