Good card game for people to play with nothing but grunts?

So long story short, I'm running a research experiment where people will be together for an hour communicating in nothing but grunts (I use "communicating" lightly).

I need to them to play a game that requires them to communicate but does not require English, and prevents them from just pointing to words instead of vocalizing. I was thinking like Uno or some other card game, but they could do that mostly without words. And charades is not good, because the people answering must also be grunting.

Thoughts?