Okay. So. In majority of occasions, it was probably safe to assume that 'oh' and 'um' was considered a quizzical, somewhat unsure response. This was clear to most people. But then, maybe most people weren't a bit tipsy, a bit in love and a bit too physically close to their best friend. Those people would probably have taken the 'oh' and the 'um' at their face value and fucked the fuck off.
Oliver was not those people.
Oliver was a fucking idiot.
So instead, Oliver thought how in this moment, this moment right there? He didn't give a shit about what was socially acceptable and even less about his utter life style of being a horrible friend that failed at friending.
Thus, Oliver kissed Charlie properly, pressing his whole body into his best friend and using the 'um' as a passage way for his tongue into Charlie's mouth.
Because, really, you either went big or you went home.