Nerd alert - this is like splitting hairs but it's a logic question and I am going to ask it.
It's an old episode so I won't say spoiler alert.
In this episode Leonard sleeps with Raj's sister Priya and tries to keep it a secret. The truth comes out when the four friends are having lunch at the university the next day and Raj asks, "So what did you think of the new episode of Caprica last night?" To which Leonard admits that he didn't see it.
The implication here is that Leonard didn't see the episode because he was engaged in coitus with Priya at the time...BUT....in the previous scene when Priya comes to Leonard she says that Raj had finally gone to bed before her sneaking out.
So...when did Raj see the episode? If he saw it BEFORE going to bed then Leonard could have seen it as well at the time because Priya wasn't with him (Leonard) yet. If Raj got up AFTER Priya had gone to meet Leonard then he would have noticed that his sister was missing.