Continuity mistake: In the beginning during the cheerleader show the cheerleader to the right of Jennifer have her left leg stretched right, covering her right knee which is also somewhat turned right, in the next shoot, supposed to be just a change of the point of view, the same cheerleader have her left leg now straight to the left.
Continuity mistake: In the bar, Jennifer stops to talk to Needy while carrying the special "9/11" drinks consisting of red, white and blue layers of liquor in tall thin glasses. Midway through the conversation the blue layer in the left glass gets about a centimeter wider when they cut to a different camera angle, then returns back to its previous level.
Continuity mistake: When Needy floats up to her cell's window she's in an orange prison uniform. Yet when she's broken out, storming across the grounds she's suddenly gained a sleeveless hoodie.
Answer: When Jen was explaining how the band members through the knife in the waterfall. When needy was walking and found the knife, the knife was beside one of the balls that the scientists were testing where the water went to. It showed the scene where the scientists were putting little red balls down to see where they came up. So no it wasn't a coincidence, she knew that was the knife.