allie-quixotic
pointed this out. And I think she's right.
I've watched Jensen hamming it up to Eye of the Tiger, oh, about 10 million times now. And after reading allie's post I've slow-mo'd through the last few seconds many times. *is pitiful*
Look at Jensen's smile after he drops the character of Dean at the end of the clip. He first smiles off to his right thusly....

Then he dips his head down (does anyone else *love* when he does that?). And he looks up to his left. His eye's immediately latch on to something and he. Just. Beams.
See?

Allie points out that this is Jensen's "Jared Smile". Again, after watching this in slow-mo several times I really, really agree. He is so looking at Jared with that smile. There is a difference between his smile to the right and his smile at the end.
And as I pointed out to fickleone, how pitiful is it that I watch these boys so closely that I recognize their body language so well that I can tell when one is looking at the other????? (Assuming I'm right, that is.)
ETA: I just have to add in that hearing Jared laughing and chuckling during Jensen's/Dean's performance--just makes this clip that much more terrific.
ETA2: Oh and btw, I so hope someone writes some fic based on this clip.