Robin tells Lily that when she tried to delete Don's number from her phone, this thing popped up that said "Are you sure?", but later, when she actually deletes Don's number, there's no such message.
Antoni Gaudí was killed by injuries received by a tram impact, not a bus. The tram didn't kill him immediately so he was taken to a paupers' hospital where they didn't treat him correctly so he eventually died three days later. In the end, false or missing treatment can be considered as the final cause of death.
In Chicago, local nighttime news is generally shown at 10 o'clock, not 11 as portrayed here.
At the end of the episode, when Robin tries to call Don but dials a wrong number, she presses only one button (instead of dialing all the digits as she "remembers" them).
The kid who beats Lylly at the karate class, is wearing the head band upside down. It says 'kamikaze'
When Ted references the death of Gaudí, he pronounces is "GOW-dee" instead of "gow-DEE." Given that Ted has been shown to strive for correct pronunciation, it doesn't make sense that he'd mispronounce a name from someone in his chosen field.
Marshall states that it was a single bullet that destroyed the death star when it was 2 proton torpedoes a fan like him would know this fact.