Caliban and Sycorax are Mrs. Baker's pet rats.  She keeps them in her classroom, so the animals are more like class pets.  Unfortunately, nobody in the class likes the rats.  

Actually, no one in the class had ever gone near Sycorax and Caliban.  Not even Doug Swieteck, and he would do anything, because they weren't cute balls of fuzz anymore. 

The rats are hideous, and they behave as if they are rabid.  

If anyone even looked at them, they threw themselves against the sides of their cage and stuck their scabby snouts out as far as they could and clacked their long yellow teeth together.  The sounds that came out of their throats were never heard anywhere else in Nature.  

That last part about the rats being like nothing else in nature is interesting.  If something isn't natural, it could be classified as supernatural. In other words, Mrs. Baker's rats might be super ugly, super mean, and supernatural.  

That sounds exactly like the characters Sycorax and Caliban from The Tempest.  Caliban is the half human son of the vicious and powerful witch Sycorax.  Sycorax gave Caliban his half human part.  His half supernatural part came from his father, the devil.  Caliban is the villain of the play, and he is described as a "hag-seed" and as a "poor credulous monster."  In other words, Caliban is super ugly, super mean, and supernatural.  I would say that the rats have been appropriately named.