So today, I PM'd the fellow whom I got Constantine from, thinking maybe there was a trick to it, maybe Con had a quirk and would only eat a certain way.
Len (the guy I got him from) said that he didn't like his food wet. And that he would get the head nice and close to the light bulb and make a nice warm target for him to 'see'.
I did that, and no sooner did I put the rat over the side of his tub, did he strike and coil!! And now his belly is nice and full!