It just dawned on me that one of the reasons animal rights people throw at reptile keepers is that reptiles don't understand glass so keeping them behind glass is cruel.
Now I've just considered that most, if not all, of my snakes know the difference between their vivs with the doors shut and the doors open. They don't need to touch the glass to know that they can't get through it, and I believe that it goes both ways, they know that the glass protects them.

What do others think? Do your garters grasp the concept of a glass barrier that they can see through but can't move through.