I think it is common. My peppermint shrimp did the same thing with EVERYTHING i've placed into the tank. It is just trying things out - if it is picking at a snail usually that is an indication (at least in my experience) that the snail is dying (assuming it isn't fighting back or anything).
I've even had mine try a taste of my BTA - needless to say it didn't like the sting!
Just keep an eye on it, make sure it isn't eating anything you don't want and make sure you are feeding it well (not overfeeding it though to mess with your tank par.)
Hope this helps!
