The first one is about Wobbuffet: the reason it is so protective of its tail is because it IS the tail. More precisely, its brain is located in what looks like the tail, which is actually its head, that's why it has eyes, while the blue "body" is something like a decoy with a fake mouth.
The second one, and I admit I believe it is true: somewhere along the development of the original Red and Green, Game Freak accidentally swapped sprites for Venomoth and Butterfree. Metapod's eyes look more like Venomoth's than Butterfree's, and (especially in the original Red and Green) Butterfree looks exactly like Venonat, only with wings, a neck and less hair. The one thing that can be used to support this theory is the fact that those versions were really badly coded, to the point where Pokémon in the game's data are in an order that has nothing to do with the official one, so I easily can imagine them making the mistake, not noticing it because the code's a mess (considering the game's development history one can assume they couldn't afford to do a lot of testing too) , realizing it only after the games' release, and then shrugging and deciding to go with it.
I'm a proponent of both of those theories as well. A related theory to the Venomoth-Butterfree idea is the hypothesis that Psyduck's and Golduck's names were swapped accidentally during development; I mean, Psyduck is the one that's actually gold-colored, and Golduck is the one that has more notable psychic abilities. It just makes sense to me.