The easiest part of the shoot for Cary Grant and Constance Bennett was the many special effects scenes, which only required them to record their lines while special effects artists made the various items they moved, from fountain pens to a pair of frilly lace panties, appear to move on their own.
Arthur Lake, the elevator boy/bellhop, went on to star as Dagwood Bumstead in the "Blondie" movies and TV series.
The fancy finned-back car driven by the Kerbys was custom built by the Bohman & Schwartz Co. using a 1936 Buick Roadmaster chassis. Originally the producers had in mind to use a coffin-nosed Cord, but it wasn't large enough. In the custom-made Buick, there were special compartments for camera equipment, etc. The Buick resembles a Cord, but the supercharger pipes on the side were just decorations. (A Cord comes with an actual supercharger.) After filming, the Buick was bought by the Gilmore Oil Co. and was used for promotional purposes for many years. It was updated in 1954 with a Chrysler Imperial chassis and drive train. The car driven by Cosmo Topper is a 1936 Lincoln Model K.
Included among the American Film Institute's 2000 list of the Top 100 Funniest American Movies (#60).
Constance Bennett was impressed enough with the property that she agreed to be paid less than her usual $40,000 fee.
Hoagy Carmichael: Songwriter and pianist, uncredited, as the piano player in the sequence where George and Marion are on the town the night before the meeting at the bank. He introduces the song "Old Man Moon", which is sung by George and Marion. (It's also sung later by Three Hits and a Miss.) It was Carmichael's screen debut. As the couple leave the bar, George says, "(Good) night, Hoagy", and Carmichael replies, "So long; see ya next time."