the only possible problem can be removing or damaging part of the mucus membrane, which protects the fish from injury and illness. Other than that, if you're gentle, and the fish doesn't mind, it's ok.

I have a cory which I think is a Herald Shultz's Corydoras ( Corydors shultzi ) but it has these wierd blueish grey eyes, and I'm wondering if it has cataracts or something. I know fish can get them, and I saw a FW angelfish with them once. Other than that, the fish is perfectly healthy and active ...