Hermies have no depth perception and yes they will walk right off of the edge of anything, and some that have done this were seriously injured.
As for running the hermie under warm water to get them to let go, as some have found out this only makes the hermie pinch harder and for a longer period of time as well due to being startled. Also, the tap water with the chlorine in it will cause the hermies gills to get blisters.
![Sad :(](./images/smilies/icon_sad.gif)
Best way to get a hermie to let go? While biting your tongue to keep from screaming quietly lay your hand on a flat surface and stay still. Once the hermie feels no movement and secure he will let go and walk off.