Ultimate versus goof?

There was one part that should be in the goofs list. When the prisioner came back to fight with the 'playmates', he was smashing a guy's head into the tree trunk, then suddenly the next scene, he got a gun in his mouth and one in his hand when he knocked another gun out of zombie's hands.

Am I correct? That is the only part that bugs me. I mean, at least show how he got the guns first then, they shouldve included the part where he cocked the gun with his teeth. lol.. I think that is a biggest flaw because the first time I saw it, I went WTF and lost a train of thoughts during the movie. Didn't the director notice it or what?