What are the odds at any given moment that the feeling is mutual?

You are sitting next to someone you find attractive, having a nice conversation while you buzz off their pheromones.

At any given moment, between any given two people, what are the odds that both are experiencing the same thing. In other words, what are the odds that the person you are with is having just a good of a time.

EDIT: mutual hetero or homo sexuality are assumed for sake of argument.