Revealing mistake: When Captain America is fighting Ultron in the truck, for a brief moment you can see a safety line holding actor Chris Evans as he's hanging on the side of the cab of the truck.
Revealing mistake: At the very last (pre-credits) scene of the movie, as all the avengers are assembling, Scarlet Witch flies in, but it's not Elizabeth Olsen but a stunt double.
Chosen answer: This is a fairly US-centric gag. In Archie comics, the titular Archie has two competing love interests: Betty and Veronica. Given the Hulk/Banner's history with Betty Ross being able to calm him down, Tony Stark has named the containment system/Hulkbuster armor "Veronica".