Salt and corrosion

I was reading a mystery novel last night, one of those cosy county house detective stories. This one was about a "how to host a murder" party gone wrong (because - gasp! - an actual murder takes place). The last chapter I read before I closed the book featured all and sundry prowling about the country house at night for various nefarious purposes. Two of the characters - Gaunt, the drunk butler, and Martin, the young man chickening out of sneaking into his secret girlfriend's room - end up crashing into each other and rolling down a staircase. I don't have the book with me, but the description ended something like this: "They rolled down the stairs and landed with Martin on the buttered side."

So is Martin on the top (like butter on toast) or the bottom (because, as everybody knows, dropped toast always lands buttered side down)?