Isinglass is a substance obtained from the air bladders of sturgeons. I learned recently that it's used to clarify cask beer, so cask beer is not vegetarian. V. sad.
The word is possibly borrowed from an obsolete Dutch word huisenblas from Middle Dutch huisen "sturgeon" and blas "bladder". Blas is from Proto-Germanic ƀlēs-, an extended form of Proto-Indo-European *bʰleh₁- (possibly *bʰleh₂-) "to blow".
The zero-grade *bʰlh₁- became Latin flāre "to blow", combining with sub "under" to form sufflāre, which became French souffler "to breathe, blow". Soufflés are so called because they are made with frothed egg white and heated until they puff up.