Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is a mystery romance (made by the director of the amazing 1980 film (The Stunt Man) in 1994 when Hollywood didn't feel the need to make every movie suitable for children - in other words, there's lots of nudity. Most of it is Jane March, but unfortunately, some of it is Bruce Willis. He plays Bill, a traumatized New York psychiatrist who flies to Los Angeles to stay with his college friend Bob, also a psychiatrist. Somebody is threatening Bob and he suspects it's one of his patients. Without describing more of the plot, I'll just say that people are threatened by masked people with knives, by mysterious cars with blacked-out windows, and by rattlesnakes.
Bill is jogging one afternoon when he returns home and opens the mail box. He's startled by a rattlesnake that lunges out after him. He falls on his back on the road and freezes in front of the open mailbox with the rattlesnake hanging out as passing cars honk and nearly run over him. Finally he realizes that the snake can't strike at him from ten feet away, and he stands up. He grabs a shovel from a gardener's truck conveniently-located nearby, and swings it at the mailbox, knocking the snake out onto the road. Then, something happens that is almost unheard of in movie scenes with rattlesnakes - he just walks away from it, letting it crawl across the road into a field. I expected him to hack it up with the shovel, but he didn't. A tip of my hat to the filmmakers. Even though they used the unbelievable cliche of a rattlesnake in a mailbox, (it's probably easier for someone to get a gun than a rattlesnake) they didn't feel the need to have somebody kill it once it was no longer a threat. A police Detective played by Ruben Blades then Jane March show up immediately afterward, but we never find out who delivered the snake mail.
I think the snake is a Red Diamond Rattlesnake, which is native to coastal Southern California where the film takes place.