The problem is that we are talking about someone who is not able to communicate. (At least that's what I'm talking about?) Probably someone who knows they should say no/stop/don't and isn't capable of doing so, because they are frozen due to fear, or because they are intoxicated, or because things are happening too fast for them to process quickly enough to react appropriately, or there are some other factors making them physically incapable of communicating a lack of consent.