Continuity mistake: The handle of the machete Jason stabs both grave digger guys with changes between shots. As he stabs the 1st guy, the handle is tripoint, but as he stabs the 2nd guy through the neck then pulls back, the handle now has a rounded end like a wooden peg.
Continuity mistake: As Tommy reaches Jason's grave, he hears laughter and voices coming from the woods. As the voices move closer we see lights in the clearing. Tommy runs off in the bushes to hide. Moments later, two guys with flashlights and shovels suddenly rush in, from the opposite left, instead of the clearing path at the right, from where they were.
Continuity mistake: While Eddie is being killed, in the second shot, there's a blood driblet on his bottom lip. In the next shot, his bottom lip is clean without any blood residue.
Continuity mistake: When Lana is hit by the axe, it hits her horizontally, but in the shot of her corpse, it is shown vertically.
Continuity mistake: After Pam runs out of the house towards the barn, she sees Roy coming, and then she trips, as she crawls her shirt sleeves are rolled up, but they weren't before she tripped.
Answer: He simply just snapped. He definitely looked angry before Joey even started talking to him, and said how he hated being there...and he already had an axe in his hands...he just lost it, and took out his anger and frustration on Joey.