We're talking snakes here, and another animals that aren't really sentient. They aren't microdosing themselves with poison or setting fires.
Sentience is the ability for subjective experience, which applies to any of the animals being discussed here. If you're thinking of something like self-awareness (a totally separate quality), you're probably correct. But that has nothing to do with the ability to learn.
There are sources for addiction regarding animals on the web. Its quite interesting what horses and goats do for some weeds.
https://en.wikipedia.org/wiki/Colorado_River_toad#Drug_use_o...
The war on Horse-Drugs should have priority. Give the DEAs some hoes to whack out the danger.