When Rob and Kit rush out of the boathouse to find Skip, Rob's wet hair turns dry.
At the end, Buck sticks the prosthetic to the side of Rob's face. But it's partially covering one eye when he runs into the room with everyone else.
When Muffy's opening her gift in her bedroom, her grip on the champagne bottle changes between shots.
As Arch dangles from the tree, the heavy boot rakes the snake aside. The floor under the dirt/grass is visible and even moves.
While 3 of the girls are in the kitchen cooking, one of them reads a question from a newspaper, regarding 'Your first time'. One of the choices is "I was ready to try again", but if this is the first time, the answer couldn't possibly be to try it again.
When Muffy says "I'm never going to forget this weekend as long as I live", Deborah Foreman isn't moving her mouth at all.
When Buffy is standing on the dining room table, one shot reveals a camera shadow on the back of her shirt.
Constable Potter is seen calling the house from the hospital Why was he at the hospital, given he was in on the prank from the start? He knew Buck was not really injured and had never been taken to the hospital.