The first such mistake I would like to draw your attention to is weevils.
"What?" you ask. "How is that a mistake? It looks like a mutant Mr. Man in Brazilian football boots!"
Yes, weevils do look amazing. Unfortunately though they are really tiny, so we don't get to enjoy the fact. In an ideal world they would be the size of horses, they would talk in thick Dutch accents, and we would ride them about, firing hallucinogenic jungle toads at one another from catapults.
This site has some amazing weevil pics anyway, including one that looks like an alien Rottweiler cyber-goth!