Which logical fallacy is used in the text?
Animals don't shampoo their fur, so it can't be good for you to shampoo your hair.

 - appeal to nature: the assumption that natural things are always good
 - bandwagon fallacy: the assumption that the popular choice is automatically correct
 - guilt by association: a negative association intended to discredit someone or something
The text argues that shampoo is not OK because animals don't use it. However, something isn't necessarily bad simply because it's not something animals use. This illustrates a type of logical fallacy known as an appeal to nature.