When you are casting any mount, try to do /dance just before the end of the cast.
The result will be that your character will turn his hands up. It's probably a buged animation. The character won't dance on his mount, he will just put his hand up (on a female blood elves it is what it does)
It's not very usefull, its just an easy way to have fun when you are afk in a city.
Everybody will be able to see the animation, but you can't keep this animation if you start to move, so you have to stay on place.
The animaiton seems different depending of the race/sex of the character.