"The Thin Man," like "The Maltese Falcon," was a Dashiell Hammett book that was brought successfully to the screen.
The studio didn't think too much of the project since William Powell was "too old" and Myrna Loy had played too many "unwifely" roles!
So what did they know?!
Myrna Loy wrote her autobiography, "Being and Becoming" (Alfred A. Knopf, Inc.; New York; 1987), and tells the story of her first entrance in the now classic "The Thin Man":
What other director (W.S. [Woody] Van Dyke) would introduce his leading lady with a perfect three-point landing on a barroom floor--even if it was the Ritz bar? I was supposed to stroll in looking very chic, loaded down with packages, and leading Asta on a leash. "Can you fall?" Woody asked. "Do you know how to do a fall?" I said, "I've never worked for Mack Sennett but I'm a dancer. I think I can do it." I would have done anything for Woody, because I was devoted to him. "You just trip yourself," he explained, "and then go right down."
He put a camera on the floor, a mark where he wanted me to land, and we shot it without any rehearsal. I must have been crazy. I could have killed myself, but my dance training paid off. I dashed in with Asta and hit the mark with my chin. It was absolutely incredible! [Page 89]
So was Myrna Loy!
Today, an actor would demand a stunt double plus medical people on stand-by on the set, etc.!
Not mention that the ASPCA and PETA would probably want a stunt double for Asta!