When Finn and Rachel are about to get married, he says "Well, Miss Hudson-Berry, everybody is waiting" and extends his arm for her to take. When it flashes to a close up of Rachel, you see Finn's lips moving, but no audio is coming out.
Toward the end of the episode, Quinn texts Rachel to tell her that she is running home to get her bridesmaid dress and will be at the wedding soon. Rachel later texts her "HURRY", which is confirmed when Quinn hears her phone go off while she is driving and looks at it to see 1 new message. Just a couple minutes later, being told that they can't wait any longer, Rachel texts Quinn again to ask "WHERE ARE YOU??". The phone, however, erroneously shows the last message sent still being the one from Quinn about the bridesmaid dress.
The goof item below may give away important plot points.
When Karofsky's father has found him after the suicide attempt, shaking the victim's head and neck is the worst possible thing you can do after an unsuccessful hanging and would likely result in death or paralysis.