When the boys are hypnotically frozen, Whitey is taken away first. When he's carried through the corridor, his mouth is suddenly open twice as far as before. (The expression on Butch's face differs between the drawing room and the basement as well, tense to slack.)
After he snookers Louie out of the hundred bucks during the first séance routine to help out Mrs. Parelli, Slip winds up collecting two hundred dollars from Madame Zola. If you watch the scene, you'll see that he got his own hundred bucks back for Louie, and Mrs. Parelli got her hundred dollars too. (The second $100 was for Mrs. Parelli's previous visit.)
A slight change in the rate shows that the "recording" of Uncle Jake is an actor repeating a line.
Questionable editing: (1) At 4:15, Slip says "Da rains came on de planes in Maine." A different camera then shows Louie entering his store, and one can hear Slip uttering his line again in the exact same way. (2) A minute and fifty seconds later, a shot of Louie opening and entering a door to the back room seems missing (possibly lost in repairing a film break). (3) At 6:15, Butch says "Louie, Louie, I didn't mean it. It's me, your pal!" Five seconds later he again says the exact same line in the exact same way. All this happens in a relatively short space in time, leaving audiences needlessly aware of film editing.