Sherlock miming Hound Dog
It's true, in the mind palace sequence when he's trying to figure out what the words mean. Check out the images at the top of this page; if you look closely enough you can see his mouth move. And try watching it closely too.
http://sc.aithine.org/sherlock/202/22/index8.html
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Dean - "I'm not happy about it. But I got to move on. So I'm gonna keep doing what we do...while I still can. And I'd like you to be there with me."
Sam - "I'm your brother, Dean, if you ever need to talk about anything with anybody, you got someone right here next to you."