They dont )
They do ask you to freestand your dog and often wave something in front of the dogs face, or make strange noises. Handler might do the same. Throw a piece of food up in the air and catch it, or use a toy, or whatever for a particular dog.
But it is pathetic.

Most of the dogs when stacked dont look at you tho, they look forward/down. Its to show the arch in the neck.

I teach my dogs to bark on command so in the ring when I freestand them and we get bored waiting I will get them to bark. And is a bit different to what most of the others do.