Sheldon has known about The Bet since the first day he met Leonard's friends, and has followed it through its various permutations over the years. He's now aided by Penny, who can be convinced to do almost anything for chocolate, but he was able to remain aware of the situation before she entered into the equation. Lesser minds always underestimate his talents.
He has exceptionally keen hearing, which helps, but neither Howard nor Raj is particularly subtle. Raj is better than most, Sheldon supposes, at least in the presence of members of the fairer sex.
Sheldon had been tempted, after meeting Leonard's friends, to have amendments drawn up to extend the roommate contract that existed between Leonard and himself, but watching the evolution of The Bet proved to be more entertaining – and useful – than not. Forcing Leonard to take his friends and their prurient conversations out of the apartment would have deprived Sheldon of the opportunity to observe them.
He's considering compiling his data for publication. It would be a fascinating study on the mating behaviors of humans under semi-controlled conditions. Penny, however, insists that it would be a violation of the central tenets of friendship.
Sheldon isn't sure why The Bet isn't a violation of their friendship – speculating on the state of his virginity and the nature of his sexual relationships would certainly seem to trespass on the bounds of friendship as he understands it – but Penny hasn't clarified that issue for him yet.
Settling into his spot and preparing for a movie marathon, Sheldon watches as Leonard puts the DVD into the player and returns to the couch, sitting three point two inches closer than dictated by social convention – and during the opening credits, Leonard puts his arm up on the back of the couch, putting it loosely around Sheldon.
Instead of protesting the invasion of his space, Sheldon leans back and lets Leonard touch his shoulder. It's not unpleasant. Leonard's hand is warm and he moves his fingers in soothing half-circles.
Sheldon shifts in his seat, moving closer to Leonard. Howard and Raj aren't here to see it, and so he closes his eyes, relaxing into Leonard's touch. Leonard's fingers tighten on his shoulder, and Sheldon smiles. He supposes that he should be grateful for The Bet, really – without it, Leonard would still be making awkward attempts to flirt with him, as if his veiled innuendos about string theory could be considered flirtation.
Sheldon had instructed Penny to bet that he and Leonard would make it to first base – and Howard and Raj had made certain that Leonard heard about it, just as Sheldon had predicted they would. He doesn't need them speculating about his virginity or whether he's ever been kissed, but he's made The Bet serve his own purposes. It really is simple, after all – a stroke of genius, if he does say so himself.
Sheldon pretends to be surprised when Leonard pauses the movie in the middle of a romantic moment and turns to him, kissing him. He waits a moment, long enough for Leonard to falter, and then returns the kiss with interest.