there isn't much verbal consent involved the first time two lovers kiss. no one asks anyone. there is just a sudden pause in the conversation, looks of desire, and then...
body language is a language. it can be used to express consent but also dissent.
if you lean in for a kiss and the other person turns their face down or away, that means "no", for example.
maybe some people have to say words and hear words to get the message across though, because they're not good at reading body language.