Lobster

That was the same thought I had. Or maybe that the lobster was somehow analogous to their situation, similar to the way a "sucker" will be superimposed over a character in a cartoon? Would appreciate any explanation of that shot.

What's the Spanish for drunken bum?

I took it to mean more along the lines of they had a large, sumptuous feast full of rich food. There's a notion, more prevalent back then, that large meals before bed, especially rich (creamy, buttery, not expensive) foods will give you nightmares. At one point the wife even says something to the effect of "we won't sleep at all tonight."