MY HANDS !
This just started last week. Last week I had my hand in the tank fixing a powerhead and BOOM ! I jerked my hand out of the tank so fast you would have thought a shark bit me ! I had no idea what happened. So I stuck my hand back in to finish what I was doing. While watching this time ! And sure enough she comes swiming up and takes a nibble and swam away as fast as she could. Since then she gives a nibble when ever I have my hands in the tank, especially if I'm doing something in "her corner" of the tank !