At the Corcorans' dinner table, the camera zooms in on Kelly eating solid food off a fork. A split second later while 'Leonard' is in mid-sentence, she and the others are shown eating soup with spoons.
Lenny first has his arm on Lila's shoulder, then off, when at the Port of Call.
In the scene in Duane Corcoran's office after the family dinner, the phone on the desk next to Mr Corcoran moves between shots.
(at around 1h 1 min) The waiter walks away from Lenny and Kelly's table but in the next shot he is back in his previous position immediately by the table.
When Lenny and Lila are lounging by the poolside before Lila's sunburn, the glob of sunscreen on her shoulder changes between shots.
Northrup Mall at the University of Minnesota, where Lenny waits in his car while listening to a weather report, does not allow cars to be parked there, nor did it allow cars in 1971-72.
When he parks his car at the beginning of the movie, the parking ticket mysteriously appears on his windshield immediately after he gets out.
Lila's speech when she's face down in bed with sunburn does not match her mouth at all. Similar mismatches happen occasionally in long shots as well.
At the Corcorans' house, between dinner and the confrontation in his office, Duane tells his family to "allow Mr. Cantrow and I a few moments alone". He should know it's "and me".