1) With everyone activating the hide non-video participants option in settings, invite one volunteer to turn on his or her webcam with you so that just two cameras are visible (side by side in gallery view). Now position yourselves so that you are standing as in the screenshot below. Now tell the volunteer that in a second you're both going to drop your hands, and when you fall to the left she should fall in the opposite direction. As long as you both stop yourselves after you go out of camera shot (and before you actually kill yourselves!) it will appear as if you're falling to the floor. See the video below for an example.

 2) Ask the participants if they can tell you which idiom they think this represents.  It's not easy to do this at all, so tell them the answer (United we stand, divided we fall) if no one knows.

3) Now give them the list of 'body idioms' below (by sharing your screen or having them written on your virtual background.) Ask the participants to work in groups (breakout rooms) to prepare their own physical performances to represent them. They could do these individually and mime them to each other, or in pairs, as in your example.  

I'll give you a hand (I'll help you)

I'm up to my ears in work (I'm very busy with work)

I'm up to my neck in it (I have a lot of problems right now)

That went over my head. (I didn't understand it)

I'm going to give you a piece of my mind. (I'm going to tell you off)

We don't see eye to eye (We don't agree about things)

She looks down her nose at everyone (she thinks she is superior to everyone else)

Biting the hand that feeds you (treating a person badly when they treat you well) 

A sight for sore eyes (a nice thing to see that cheers you up)

He gave her the cold shoulder (he ignored her)

4) Now invite everyone back to the main room. Make sure the written versions of the idioms are no longer visible. Ask different groups to show one or two of their idioms for the others to guess.