Actually, they have killed rats: "the dose of THC which kills 50 per
cent of animals (LD50) when administered intravenously is 40mg/kg in
the rat but 130mg/kg in the dog and monkey (Rosencrantz, 1983)."
Yes, it was administered intavenously, but it did kill them.
I have not (yet?) found citations about what the LD50 dose would be when ingested. It also depends on what part of the plant is ingested, as the leaves, and especially the stems, seem to contain much less THC than the buds.
The stems are also highly fibrous, that's what people used to use to make hemp fibers for ropes and clothing.
Andreabaylon, did you notice any effect on Nibbler? Did he show any signs of being affected at all?
I guess the best thing to do here is keep an eye on him, and check for any signs of GI slowdown etc.