I need a sex-scene vocabulary lesson...

Forgive me if this is a stupid question, but another thread got me wondering about this and I realized I had absolutely no idea about the answer.

Basically, is there such a thing as a bisexual sex scene with only two participants?

I always thought of it as:

M+F = straight sex scene.
M+M = gay sex scene
F+F = Lesbian sex scene.*

However, what if one (or both) of the individuals is bisexual? Does that make it a "bisexual sex scene" or is the scene defined by the genetalia that's present during that particular encounter?

Thanks in advance for the vocabulary/terminology lesson.

*This is assuming that the scene in question does not contain any hermaphrodites, which brings up another question: is there a special term for hermaphroditic sex scenes?

Ahh, that clears it up. I figured that was probably the case in film, but I wasn't sure about literature, where it's much easier to convey the character's thoughts and emotions even when they're not speaking.

Thanks!