Continuity mistake: When Art is eating breakfast at the Peterson's house, he takes items from the fridge. Watch when he comes back over and talks to Ray. The position of the pineapple under his arm changes from shot to shot. (00:10:40 - 00:11:25)
Continuity mistake: This makes the second time that this mistake - discussed earlier - occurs. After Klopeck's house blows up, Carol Peterson drives back into the neighborhood to notice all the commotion. The first camera shot (shown from inside the vehicle) shows the front passenger's head rest to the seat is missing. Next camera shot (shown from the outside of the vehicle) shows the head rest as being back on the passenger's seat. (01:25:10)
Continuity mistake: At the Klopecks, the bonfire of 'romantic' candles changes with each shot, from big candles to severely melted ones back to full ones again, a few times throughout the scene.
Continuity mistake: When Art jumps the fence to Ray's property to escape Landru, the Great Dane, his feet break the alarm trip wires as he falls. Later, when Art, Ray, and Mark are going over the fence after Art cut the power, the alarm trip wires are intact again.
Continuity mistake: When the garbage men are first seen discussing attending the healing seminar or taking on Roselli plumbing, the house in the background is different from the house on the street across from the Klopek's house which is then seen after Art, Ray and Rumsfield go out to question them about the trash.