Where most episodes take place over a few days, this one takes place over a month, as mentioned by Raj, and illustrated by how Sheldon managed to grow a mustache and Raj to learn sign language.
Penny is wearing a Captain America t-shirt towards the end of this episode.
Raj has a date with Emily, a deaf woman (played by Katie Leclerc, who is hard of hearing in real life due to Meniere's disease). In The Desperation Emanation (2010), he had already claimed to be dating a deaf woman, though later admitted in The Boyfriend Complexity (2010) that this was a lie as he hadn't been kissed in over a year.
Title reference: Raj getting hooked up with the deaf Emily is the catalyst for the use of American Sign Language, which involves a lot of "wiggly fingers".