It was after the taping of this episode had wrapped that the cast and crew performed a flash mob to surprise the producers. The flash mob was choreographed by Kaley Cuoco's sister, Bri. At first the cast pretended to not know what was going on, but quickly joined in the dance, with the exception of Jim Parsons; who at the request of Kaley, stayed in character through the whole thing and once everything settled down, uttered his trademark word, "Ba-zinga!".
The show's most-watched episode ever in the US, with 17.4 million viewers.
This is the first time that Penny actually tells Leonard that she loves him, though admittedly it was accidentally. A somewhat reverse situation happened in Season 3's The Wheaton Recurrence (2010) when Leonard says it to Penny, and she responds, "thank you."
This is the last episode to just feature the 5 original cast members.