we have never seen it move, only time we saw it on the glass was in the middle of the night, and it was already up there, as shown in the above pics. we turned on our moon lights and it didnt move at all, so we got those pics. its shell is like a mussel it closes up tight. just like the kind you would buy in the store. im SURE its not a snail, unless a snail took over a mussel shell, so far we have seen 3 of these little guys, and they seem to only move around at night, and only open at night too.