Question Eleven of Chapter Nine of the Third Decade
Whether it is lawful to charm serpents or another genus of animals
It is asked whether it is lawful to charm serpents or heal animals by incantations.
It is answered that, if in incantations of serpents or any animals whatsoever regard is had only for sacred words and divine power, it will not be unlawful.
But for the most part such incantations contain unlawful observances and obtain their effect through demons, especially in the case of serpents, because the serpent was the first instrument of a demon for deceiving a human being.
These things are from Thomas in the place cited above, in the reply to the third argument.