What you are calling a "two-headed monster" I have historically called a gemini, which is a term I learned from a friend who does square dancing.

Is there a term for an eye-contact hey? The hey where you and your partner keep eyes locked, so one of you has to do the hey backwards?

I've also heard chaos used to refer to the specific act of role or partner switching within a chaos set - "Yeah, she was dancing with john a moment ago, but then i chaosed her into the next couple down so now he's my partner."

Also, a few that occur to me...

Sharing a partner: When you and another person agree to trade off dancing, say, the follow(but if could be either role), while your partner dances the lead. One of you looks for a good moment within the dance when one follow can step into the set and the other step out. At that figure, *every time that figure rolls around in the dance*, you switch which follow is in the set and which is standing by the set watching and waiting for his/her turn. This results in each follow dancing every other repetition of the dance. Like the gemini/two headed monster, this is a good option if you double-book by accident, or if you really just want to mess with people's heads a little.

Sleazing: Also known as sleaze swinging or blues swinging. It's the act of substituting a slower, close-contact, more consciously flirtatious swing, a la blues dance, for a standard swing.

Cheating: Most commonly, the act of grabbing a quick swing with your partner, your neighbor, your shadow, someone from another set--anyone really--anytime when the dance isn't to have one. Substituting a swing for a courtesy turn is cheating, for instance; so is the twos grabbing a swing while the ones promenade down the hall.

End effects: any special maneuvers you do at the end of a contra set, especially if you're supposed to be out, to make the dance continue a little more smoothly for the other couples dancing.

Side effects: any flourishes or other maneuvers you do with someone from the next set over. If the men are alemanding in the center and the women reach out to alemande each other between the sets, for instance, or when you back extra far out of a wavy line in the center to form wavy lines in between the sets, it's a side effect.

I sort of feel like there should be a term for when you're out but you find ways to step back into certain moves in the hands four nearest you, like following someone to create a hey for five, or joining in on a circle left/star right--but i don't know if there is a word for it.

A few of the regular figures i've occasionally heard given special names in some areas but not others, such as the gypsy meltdown and the pass-the-ocean.

A couple other useful ones that aren't actual dance moves and therefore may not fit...

Tefloning (pr. TEFF-lahn-ing): When you're looking for a partner for the next dance and someone glances at you then carefully looks over your shoulder, pointedly avoiding eye contact so you won't ask them to dance, you've just been tefloned.

Contranental drift(or simply drift): when a contra set slowly slides to one side (or up, or down) over the course of the dance.

Mis-four: when you take hands four, only to realize that someone made a mistake up above and you need to retake hands four with a different couple. As in, "Yeah, sorry, we misfoured. you'll get to dance with them later, but for now you're in my hands four."

Ghost: that partner or neighbor that you should be dancing with right now, except someone's run to the bathroom or something. Most common in walk-throughs. If you do the figure anyway as if that other person were there, it's dancing with a ghost.