Revealing mistake: When Lily brings out the "leaking" beanbag, you can see that she has the little white pellets in her clenched fist and is dropping them periodically, making it seem as if they're coming from the bag.
Factual error: When Ted recalls his trip to Spain the map onscreen is full of spelling and geographical errors: Marida appears in Portugal but it's in Spain and should be spelled Mérida. Valencenia = Valencia; Tarrogona = Tarragona; Grenada = Granada; Pamplona is placed where the city of Bilbao is; also Sevilla is placed 140 kilometers to the left of where it really is.
Chosen answer: In a flash forward scene in Season 8, it shows him with his first born: a daughter.
XIII