Thanks, Nonsuch.
Not only was the horse-racing banter invented for the film, it was invented and shot well after the rest. The first version of the film was completed in 1945, but not released for various reasons. By the time the studio was getting ready to release, Bogart-and-Bacall had become a real-life thing and they wanted to increase her role and the couple’s screen time together. That scene was added, along with quite a few other changes, and it was released in '46.
And that may be why the plot is so full of holes and questions - the stuff that got cut out so they could have more B&B might well have included some plot points.
In particular, the screenwriters put Vivian into two scenes she’s not in in the book: the one at Joe Brody’s apartment, when Carol Lundgren kills him; and the one at the hideout with Eddie Mars’ wife. The last one isn’t actually so bad — it’s probably more plausible to have Vivian free Marlowe than Mona Mars, which is what happens in the book — but putting her at Joe Brody’s apartment doesn’t really make sense, since she shouldn’t be aware of anything concerning Geiger, Agnes or the dirty-books racket.
They were talking about horse racing? Boy, it sounded a whole lot more interesting than that!
Ain’t that the truth? Lauren Bacall as she was in The Big Sleep and To Have and Have Not…damn.
I don’t do celebrity crushes - I can count every one I’ve ever had on one hand without running out of fingers - but she’s one of them.
From Bacall’s autobiography, By Myself (p.121):