This is one of those things that's just for fun. I just rolled a Druid so I didn't know about this. I'm sure a lot of people do cause it's very simple so I'll keep this thread nice and simple.
1) Go into animal form (Cat, Bear, Travel, etc)
2) /dance
3) Hearthstone
When you Hearth while dancing as an animal you will come out of animal form to Hearth but your Druid will still be dancing.
For those of you who didn't know this, Enjoy!