Throughout the episode it's stated that the dead grandmother that's dug up in Sheila's mom, but the tombstone says "Broflovski." That would make it Gerald's mom.
The color of the little islands on the lake changes from time to time.
The color of Fieldy's bass guitar changes between shots.
Cartman blows up the Antonio Banderas doll through the penis, but the plug appears by the left foot.
Between Halloween and Christmas, there are 55 days of shopping, not 72.