Instant TERROR......just add water! An earthquake out in the Salton Sea awakens the creeping dread, gigantic vampire water snails are on the loose and they are hungry for human fluid! Just about the right side of good, The Monster Who Challenge The World holds up well because of the well constructed creatures and a bit of care and attention to the boffin discussions. Far too many 50s creature features just used a basic premise of creatures obliterating mankind because they were in an odd mood, but much like The Beast From 20,000 Fathoms, this picture at least takes time to give us a bit of a nature heartbeat to help us understand the methods of a mollusc, and that alone should be applauded, so we learn while we have fun so to speak. The cast ooze B-movie standards, and that is in no way a bad thing here, whilst the Catalina Island locale sequences are pretty nifty to help salt the beef as it were! Good honest fun that isn't short on creepiness, and top marks to the makers for introducing a very ingenious creature to a truly wonderful genre. 6/10