Raj, Sheldon and Leonard heckle Stuart from Sheldon and Leonard's apartment window, yet Stuart is shown near the front doors of the apartment building, which is on the opposite side of the building from Sheldon and Leonard's apartment. This scene would only make sense spatially if the three hecklers were in Penny's apartment, which is on the same side of the building as the front doors, yet even her apartment likely doesn't have a window on that side (one is never pictured).
When Sheldon, Raj, Stuart and Penny start to watch "Game of Thrones" in Penny's apartment, the audience briefly sees the back of her TV. There is a blue cable plugged in and it's an Ethernet cord used to give the TV access to the internet, but it's been very well established that Penny gets WIFI from Leonard and Sheldon because she asks several times what the new password is.
Sheldon claims that, in Italian, the "morta" in mortadella means death. It does not. It comes from the Italian word "mortaio", which means mortar. Mortars were used to grind pork meat into the emulsion used to make mortadella.
In the final scene, as Stuart rides away on the bicycle, his cloak becomes tangled in the rear wheel sprocket and chain. This would lock the rear wheel. As the crash is shown, Stuart high-sides over the handlebars which could happen only if the front, not rear, wheel locked up.
At 5:54 in & 5:57 in Penny (Kaley Cuoco) looks right at the camera for a split second.