Me neither but we're never really going to be able to provide the varied wild diet of some animals though and so the vitamins compensate for that. Think of horned frogs, a big part of their diet is other frogs (including their own)... To feed them other frogs in captivity isn't feasible considering frogs go for more or less a tenner each. People feed fish and pink mice to compensate for the calcium they'd get from this but pink mice are fatty and fish can be diseased.