This episode was filmed the day Carol Ann Susi (the voice of Mrs. Wolowitz) was announced to have passed away. Most of the studio audience didn't know due to waiting around outside all day, and the cast did an outstanding job of getting through filming like true professionals. After filming, it was announced to the studio audience and many tears were shed.
Professor Sharpe was played by actor Paul Willson who was known for years for sitting on the end of the bar in the sitcom "Cheers".
During the highlights of 'Fun With Flags', the image that appears in between the sections is the Apartment Flag of Leonard and Sheldon's room (a gold lion rampant on a field of azure).
Third and final appearance of LeVar Burton as himself.
Sheldon agrees to erase LeVar Burton's contact information while Burton is watching. In the show's history of Sheldon's report with celebrities, this actually qualifies as one of the milder ways of how he parted ways with one of them. Throughout the series, Sheldon has ended up (in)advertently annoying or insulting celebrities such as Steve Wozniak, George Smoot, Neil deGrasse Tyson, Bill Gates and Stephen Hawking (although he eventually developed a sort-of friendly rivalry with the latter). He has restraining orders filed against him by Leonard Nimoy, Carl Sagan, Stan Lee and Bill Nye. Lastly, in The Russian Rocket Reaction (2011), Sheldon mentions his list of 61 "mortal enemies", which includes Joel Schumacher for ruining the Batman saga and Brent Spiner for ruining his Wil Wheaton action figure (Wheaton actually got moved off the list due to giving him said action figure).