By their nature, tatzlponies see absolutely nothing unusual about cuddling up inside one another. It allows them to fully embrace their friends, family and loved ones in a full-body entanglement of tentacles, limbs and the soft, smooth, cushy walls of their crop.
 
Aside from being a little stuffy, its pretty much the most comfortable place you could ever want to take a nap, lulled to sleep by the sounds of their heartbeat and breathing. Tatzljack certainly doesn’t mind giving her little sister a nice safe place to sleep. If I had the patience for drawing comics/series I would totally have included something of her sliding herself inside.