I think Parker [the older of my two ferrets] is learning how to negotiate consent despite being nonverbal [being a ferret and all]. Like everything she does, being the cutest thing to ever cute, it's adorable.
See, ferrets like to play quite rough, and since we brought Alec home and she has another ferret to play with, she's escalated the roughness of her play from where it was when we first brought her home, even after she healed from her surgery. Watching the two of them play looks exactly like those scenes in cartoons where you see a tangle of limbs poking out every-which-way with no actual identifiable bodies, and there's a lot of teeth on necks and the like. It has a fascinating rhythm to it which I can't quite explain right now.
They also like to play with me in exactly the same way, roughly as though my hand and forearm were a ferret to play with. I think Parker at least has decided that the fleshy area between my thumb and index finger is my "neck" for these purposes, and that's usually what she goes for when she tries to bite me.
The interesting part I've noticed recently is how she bites me. The first time she gets me, she'll completely freeze with her teeth just barely touching flesh, as though waiting to see how I'll react. If I continue to play, or even just stay still, the next time she'll bite harder. Around the third or fourth time it's usually enough to cause a bit of pain, but if I yelp and jerk my hand away she backs off. Actually, she usually backs off on the rough play entirely for a bit, but then will come back at a less bitey/less strong bitey level.
shield_toad111 once told me about a technique for training puppies not to bite too hard involving yelping and then leaving and sulking if they bite you enough to hurt . . . that this is how they would learn their limits when playing with other puppies in their pack. I'd kind of decided to try something similar as soon as we brought Parker home, and in retrospect I think it had a positive effect, as she now seems to be actively seeking those signals from me.
Obviously, words are less ambiguous and allow you to negotiate before you reach the limit rather than when you're at or have just crossed a line, but it's really neat that my ferret has developed a model for determining what sort of play is appropriate in the moment and minimizing harm while playing in the way she prefers. And of course if I don't want to play bitey-tickly in the first place, I can decline to respond when she bounces around excitedly at my feet, and she'll find other entertainment.
Addendum: [A quick shower tells me I should add this after all] Parker does not represent the Gold Standard for enthusiastic consent by any stretch of the imagination. But something to think about: are you worse than my two-year-old ferret at making sure the people you're playing with want to play with you, want to play with you in the way you're trying to play with them, and are still enjoying playing with you in the way you're playing with them?