When Blaine sings the song Somewhere Only We Know to his boyfriend Kurt, at about 1:25 into the video you can see Brittany step down the step twice as the Warblers give their good-byes to Kurt.
When Lauren is talking to Quinn about Quinn's past she doesn't know what Quinn's old nickname was, and Quinn tells her. However on the poster it already has her old nickname on it when Lauren doesn't even know it.
Santana accuses Brittany of not having reciprocated the "I love you" previously, but Brittany actually did say she loved Santana in the earlier conversation.