What's the stuff near my tonsils?

Whenever you poke your tongue out, there are these flaps of skin, in front of your tonsils, that stretches. I always find little yellow/white soft things in between the skin and the tonsil. I usually get it out with my finger in the mirror as it can be quite frustrating trying to get it out with your tongue all day. What are these things and is it unhealthy? Can I prevent it?