As Grandpa Lou is checking out at the supermarket, a lobster rips off the cashier's bowtie, but in the next shot his bowtie is back on.
When Didi puts Tommy in the crib in "Weaning Tommy," when the viewer still sees Didi, the pillow is in Tommy's crib. Then, when the camera zooms in on Tommy, the pillow disappears, only to reappear when the camera angle changes back to where the viewer can see Didi.
When Didi is on the phone with Betty, the hand on her waist is backwards.
The clock in Tommy's room has no hands.
When Lou first begins adding up his total with the calculator he says that the cost of the Fudgy Ding-A-Ling Bars is $2.79, but the price displayed on the shelf was $1.25.