Every game I’ve played is full of non intentional communication in addition to timing and that’s part of the game play as far as I’m concerned. Even the way you move your hand communicates something.
Indeed, I think it’s impossible to have zero information at all unless players aren’t even in the same room. There’s just too much meta information you can feed off of.
I feel like this is the part the other comment or is either ignoring or not seeing. We’re not talking about non-verbal communication, like the hand signals of a 3rd base coach. Of course it’s forbidden to hold up fingers for the numbers on the card you have.
That rule doesn’t forbid your natural actions and reactions.