Revealing mistake: When Shooter pins Mort against the tree with the shovel, you can see that it's a rubber shovel because it's bending around Mort's neck. [Mentioned on commentary]. (00:40:45)
Trivia: When Mort smashes the shower door, the hole left in the glass looks like a small, four-legged animal with a screwdriver in its neck - which is how Shooter kills his dog.
Chosen answer: An additional reference to the full dominant personality takeover of Shooter, everything gravitates South Mississippi.