Penny compares Sheldon and Leonard's relationship to the Sesame Street (1969) Muppets Bert and Ernie. She once mentioned that as a little girl she wanted to marry Ernie and calls Leonard "Ernie."
The second time there is a glimpse of Howard's mother. The first was an overhead shot of her in a pink outfit in Season 5's The Countdown Reflection (2012).
Penny admits she loves Leonard for the first time without doing it accidentally.
As well as being one of the first times there is a glimpse of Howard's mother, it is also the first time she speaks normally without shouting from a distance, when she has just made a meal for Raj.