coming across a human skull in your backyard=creepy. (well, maybe not, depending on who put it there/your tastes)
Poss. derivation from Fox Mulder's nickname on the X-Files because Mulder embodied an outsider ideal of sorts being cute and smart and totally committed to his world view even when it was constantly under attack by all the "normal" people.
J: "Yeah, it's spooky."