The trick of taxonomy is basically figuring out what

There is no trick to it. If you look up the word in the dictionary it means "the branch of science concerned with classification, especially of organisms; systematics". So, in biology taxonomy is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups.
Hope that helped

Control variable- changedependant variable- stays the samechanging- food itemsdependant- presences of proteins