When Tracy is speaking to the Detective Russick about the McCann case, in the close up shot she has frozen her phone, in the long shot the phone is no longer frozen, and then switches back to being frozen again before she drops it.
Dr. Zimmerman tells Tracey Strauss that she was one of three identical triplets, Nikki, Tracey and Barbara. This is sometimes viewed as a plot hole as people mistakenly view Nikki Sanders' split personality 'Jessica', from season 1, as an actual twin sister. In truth, 'Jessica' was named for Nikki's adoptive sister, who was killed by her adoptive father when they were children (causing Nikki to repress the trauma and develop split personality disorder).
Future Peter is killed by Claire, not because he never absorbed her power to heal (he did in the first season) but because the Haitian blocked his regeneration power. Claire knows that she can definitely block it by putting something in the back of his neck, like hers was blocked by a piece of wood in season one. She even tells the younger Peter she can kill him with a bullet in his neck.