Amy's clearly well-versed in Feed Dumpology if she guessed off the bat that it was drug-related mushrooms.
Also, I'm not sure what the problem with the origin of the mammoth fossil is. Yes, they used slaves to dig it up; they used slaves for everything back then. Shoving all the stuff that doesn't have a pristine historical record under the rug would make for a lot of very empty museums (heck, the British Museum would be spotless), as well as painting a false picture for modern people. Better to acknowledge it, warts and all, than to not acknowledge it at all.