Percula clown "cuddling" rock?

[Lil' Horned Blenny]

My Percula has been "cuddling" one certain rock in my tank. To describe it better, he looks like he lies on the rock then goes into spasms/fits, which it does on both sides. The clown has also done it when another fish swims past. Is the clown just being protective of its rock and treating it as an anemone or could it be distressed and otherwise trying to scratch itself? The rock is very smooth and the clown has no marks and behaves otherwise normally, all parameters are normal

[jenglish]

Sounds like he is hosting a rock. Clowns are nutty like that, they will host inanimate objects, even if their is a host anemone sometimes. I would not be concerned.