When Barbara is curling her hair and Richard is cutting his toenails, the viewer sees Barbara from behind and her reflection in the mirror. There are clearly two rollers pinned to the top of her head. Richard cuts a toenail that lands on Barbara's vanity table. She is shot from the front and she flicks the toenail off the table with no rollers on her head. In the next shot from behind again, the rollers magically reappear.
In the bathroom, Richard accidentally sprays water all over the mirror with when he fumbles with his Waterpik. Then Barbara walks over to the mirror and it's clean and dry.
When Richard goes to Nancy's house the night after he finds out that Barbara is dating Al, the angle of Richard's shadow on Nancy's door changes between the long shots and the close-up shot.
When the lady hypnotist turns toward the audience in the nightclub, a puff of cigarette smoke goes in reverse.
When Richard is bowling with the kids, he gutters the first and second balls. The pinsetter picks up the pins on both shots. (It should have knocked the leftover pins down and reset them after his second gutter ball).
When the last car leaves the park scene, the car door slam doesn't match the sound.