These little machines were an early investigation of "Artificial Life".
They were phototropic — i.e. they would notice any moderate light
source in their vicinity and move toward it. Brighter lights they would avoid
— until their batteries were running low, at which point they would find
the brighter light on their 'feeding hutch' suddenly attractive!
The University of the West of England has much more about the creatures
The other link I used to have on this page has died, but I suggest a google search for "Grey-Water Tortoise" or some such to find some of the interesting stuff on the creatures currently available on the web.