Maybe psychological problem?

I have a friend, and he is worrying me. He was showing off a portfolio of his photography, and all of them (apart from 1) were pictures (close up, mostly) of dog ****. I didn't know how to react, and I still don't know if it was a joke. He did seem to be serious. He said that he captured all aspects - smooth, small, big, hard, wet, bitty etc. Should I get him to talk about it seriously?