Someone will undoubtedly make a case for the alligator on a leash, the raccoon with a litter box and the backyard bear, but most will agree that there are animals and certain slithery reptiles that simply aren't suitable pets.
Sometimes an employee simply isn't a "fit" for the job he has landed in. Whatever the reason for the mismatch, it will strain patience and adversely affect productivity. If the square peg can't be trained into cylindrical shape, let it go.
Unless the cubicles display signs listing the diet and Latin name for each department, keeping the untrainable is bad business.