We taught one of our dogs to sing, on command. Whenever he heard a siren, he would throw back his head and howl. By repeating his name and the word "sing" while he was doing it, we eventually had a dog who would throw back his head and sing on command. Kids loved seeing him do it.
Most of our dogs were taught to relieve themselves on command using the same method. While they were *going,* we would say "Lobo, hurry up" or "Ranger, hurry up" during the process. After a while, they got the urge to go when they heard the phrase. It was a convenience to take them outside and use the command just before we went to bed ourselves. Or in the rain, it was especially useful for a quick out-and-back-inside.
One would not think this would work on cats. It does, after a fashion. BigEd tells Mew, "time to go to bed." She will run to the room where her sandbox is, use it, and then demand to be let out of the room. Thereupon, the used sandbox would be cleaned. I am not sure who trained whom, however.
Clean sandbox goood ... for everybody.