Newbie Anemone Question

[k_jenkinson]

I bought a green bubble tipped anemone last wed. and it was doing great in my tank for a couple days but yesterday i noticed that it had shrunk down in size flattened out all its tenticles <- farely normal i know but it also opened i'm assuming its mouth to about an inch and a half and i can see inside of it but can't see rocks. After about a four hours he went back to normal but when i came home from work he had done it again. Just wondering if its normal and why he does it. Thanks