In the forest when Peter gives JT a head start, JT stumbles into the river and heads upstream. The next JT scene shows him running - downstream. Peter arrives at the river and also turns upstream, but the very next scene shows he is moving downstream.
Near the end when being hunted in the woods, he is running in a stream his directions changes from up to down stream several times.
When the knife is first plunged into JT's hand and the next shot after, it's not embedded nearly as deep as subsequent shots show it to be.
After Katherine calls the police, she does not return the phone to the cradle. However, when she returns to the house, the phone is back in the cradle.
When the detective Coley is following Peter on the highway, as he makes a lane change, you can clearly see a passenger (cameraman?) in the back seat of the Volvo.
In the beginning, after Peter is fired and he is making dinner, he is handling the raw chicken, then without washing dips his fingers in the small spice dishes (salt & pepper) - no professional chef (especially one as "pretentious" and meticulous) would do this, as it could contaminate the spices with e.coli, etc.