Revealing mistake: When Four injects Tris with the serum before taking the test for the first time, it is very apparent the syringe is not injected into Tris' neck. The tip of the syringe is merely just touching the skin of Tris' neck and the syringe is shown moving around her neck. (01:07:30)
Revealing mistake: Natalie Prior appears to be breathing when she's dead.
Revealing mistake: At the end of the first fighting session, after Tris' opponent has Tris on the ground, Eric gives Tris the signal to get up and the opponent punches her one last time. It is noticeable that the final punch does not hit Tris, but she still reacts anyway. (00:36:15)
Answer: There aren't really obstacles. On a zip wire, there isn't really much scope for manoeuvrability. You follow the wire.