That is actually well known (relative term, I’m sure). But in the context of the movie, and perhaps to slip something past the censors, it was the sled.
On a side note, - whoopee - I get to be a Cafe Society wonk and say that that’s where this thread belongs.
I am a bit skeptical about the gore vidal explanation…how does he know? I think that he is one of the most brilliant writers that the earth has seen, but this one seems as if he is pulling someone’s leg. Did Marion davies tell someone? vidal seems to go for the easy ones quite too often for someone with his panache!