Cal is more persistent than people tend to give him credit for, that's how. Sherlock needs the occasional dose of normality even more than Cal does, and that's really saying something.

He brings the Holmes DVD over to hand it to Sherlock, saying,

"I brought the one you had picked out (http://americas-son.livejournal.com/1290.html?thread=127754#t127754) before, and the sequel." Because he really, really doubts that Sherlock owns any normal movies. They're probably all like, documentaries and French movies and all that other smart people stuff.