When Juliet first sucks a bullet out of Rigby, she wipes off her lipstick first. After sucking out the bullet, she's wearing lipstick again although she never reapplied any.
At 44:20, when Rigby is making shadow plays with the wooden ducks, the position of his hands does not match that of the shadows on the wall.
Kitty Collins ditches her brooch into a plate of soup, Rigby opens the brooch and pulls out a paper, which would be soaking wet but is clearly bone dry.
Everytime Juliet sucks a bullet off Rigby's arm it comes out with its rounded tip pointed inside Juliet's throat and the bullet's flat base is shown on her teeth. It should have been the other way around.
Field Marshal Von Kluck's (Carl Reiner) collar insignia are on the the wrong way. The right tab should should be on the left side and the left on the right.
In the grocery store by the boxes of Farina, in the shot with Steve Martin, the baby on the box is facing the left of the box. In the shot from Double Indemnity with Fred MacMurray, the baby is facing the right side of the box.
When Rigby is sitting in a chair with a drink while talking with Huberman (Ingrid Bergman)the film was reversed during editing resulting in Rigby appearing as a mirror image. Specifically, holding the glass in his right hand with his breast pocket and pocket square appearing on the right hand side of his suit, instead of the correct, left side. Between cuts, the image reverts to normal.
After Rigby kills Field Marshall VonKluck, his body falls across the table. In the following scene, his body can be seen in the background and he is still breathing.
After drinking the "Micky" , Rigby is in the bathroom to shave his tongue. The electrical outlet next to the sink is a modern grounded (3 prong) model that wasn't in use until many years after the movie's 1946 time period.
Rolodex card file wasn't marketed until 1958, yet appears on a desk in scene set in Forties.
The newspaper in the opening scene has a large headline saying "Dodgers Lose Again." But that wouldn't have been a big deal for a Los Angeles paper in the 1940s -- the Dodgers didn't move there from Brooklyn until 1958.
When Rigby is talking on Juliet's phone to her sister Leona, the handset and coiled cord to the phone are from the 1960's-80's, and not the straight cloth-covered phone cords in use in the 1940's when the story is taking place.
At one point Reardon references the Kinsey Report; the first volume was published in 1948, but the movie is set in 1946.
In the scene with the pigeons after Juliet leaves, Rigby says "after a half bottle of bourbon..." and Jack Daniel's Tennessee Whiskey is pictured. Jack Daniel's is not bourbon - it never has been and never will be.