Here is a vintage bottle of real snake oil. A snake was put in the bottle, along with some unknown liquid, back in the 1880s.
A bottle collector dug it in Oregon, up in 2007, and found that it contained an unexpected surprise:
and a closeup of the snake within the bottle:
I suspect that the bottle was filled to the top, back in the 1880s, and that in the intervening 120+ years, it slowly leaked out most of its rather noxious contents.
/ed B