At the time of filming Josh Radnor (Ted) and Lindsay Price (Cathy) were "literally" dating. This was the 4th time that the "significant other" of a regular cast member had a guest appearance on the show. The others were Alexis Denisof (Sandy Rivers), Taran Killam (Gary Blauman), and David Burtka (Scooter).
At the episode "Spoiler Alert" in which Ted is dating Kathy (the one who talks a lot), she mentions during dinner that she knows a place at the South Bronx which has the "best cannoli in town", which is the same place Ted took Robin on their first date.
Cathy's name and her flaw of excessive talking are references to the doll and phrase 'Chatty Cathy'.
The plot highlights Robin's (Cobie Smulders) habit of using the word "literally" instead of "figuratively". In the web-series A Series of Unfortunate Events (2017), which also starred Smulders in the first season, Neil Patrick Harris's character Count Olaf always uses these words wrong.
Marshall continues writing in his Blue Book after time is called on the Bar Exam. In many jurisdictions, the is enough to have that book thrown out and all the information disregarded. Marshall would have known this and likely wouldn't have done this. If he did do this, it's unlikely that he would have passed.