I don't see how a SFE could eat a snail?? Mine has problems with large pieces of raw shrimp. (12-14") They could not
IMO suck out a snail.. If they could crush the shell then they may be eating them.
Mine gets fussy every so often so I try and mix up his food when he does. Try fresh uncooked shrimp cut into small pieces and feed to him on a feeding stick, get the shrimp from the supermarket.. I also try scallops every once in a while when he gets fussy.