When Isaac crawls back behind the wall after collecting the radio from the dead marine, the wall with the door opening is completely demolished by the sniper. A moment later the door opening is mysteriously back again.
During a scene where the main character is overhearing radio chatter, some one says "over and out" which is incorrect radio procedure. "Over" means "my message is finished and I am waiting for your reply." "Out" means "I have finished talking to you and don't expect a reply." One would never say "over and out"; one would either say "over" to continue a conversation or "out" to end it. Any military personnel allowed on a radio would know this.
Early in the movie when Issac is removing blocks from the wall to make an opening to look through with his scope, the blocks fall and crush his hand, specifically his right index, or "trigger finger". That finger is shown bloody and misshapen, possibly broken, for a vast majority of the remainder of the movie. At the end, he is able to make a shot at the enemy sniper using that same finger and it is shown to be uninjured. Precise trigger control is critically important to making accurate shots, particularly for a sniper. Making a long range shot like that with an injured or broken finger is highly unlikely.