Some scuba diving moments in movies are hilariously unrealistic. In “Jaws,” a scuba tank explodes like a bomb, which is impossible. “License to Kill” shows James Bond ascending rapidly without risking decompression sickness, which real divers know is dangerous. “The Abyss” features a liquid breathing apparatus that wouldn’t work as portrayed. “The Cave” has divers conversing easily with in-mouth regulators, which shouldn’t be possible. Lastly, “Journey 2: The Mysterious Island” shows characters using homemade air systems that wouldn’t function correctly at depth.