The following contains a detail that might be a spoiler for one scene in the movie John Wick 3, in case you care about such things. There are some dogs in the movie that do their own stunts, no CGI, where they bite people in the crotch. How does one train dogs to do that, especially when there's gunfire, people running all around, some with cameras, and you're just a dog who doesn't understand movies, much less doing a scene over and over? And how do you ensure that the bites don't hurt the actors? Director Chad Stahelski tells the story of the dog actors.
...most of the time you see animal stuff, the trainers are right behind the camera, or just out of frame so the trainer can control the animal and give the commands. We couldn’t do that, so the only way to do it was to have an on-camera trainer. So we literally had Halle (Berry) go for two to three hours of dog training every day — where she was actually coaching them, training them, commanding them. When Halle is on screen, that’s her actually giving the commands to the dogs. And that just takes a massive amount of time. Like we would say, there’s no such thing as a movie dog. You get a dog and you have to train it from scratch. So we took notes from how the military trains their dogs, how SWAT teams and bomb-disposal units train their dogs. We kinda took those methods and ran with it.
Read how the dogs were trained over seven months specifically for this movie stunt, at Uproxx.