When Sean is about to leave to take Amanda to the hospital, Tyler says, "Call me when you get to the hospital". But earlier it was established that there were no phones in the house, and there was no cell service there either.
During the heated discussion, one of the young takes the rifle and dumps a boxful of rifle cartridges on the hearth. The rounds make a bell-like sound, indicating that they are empty casings. Loaded cartridges would normally make a dull clunk or thud.