Final answer:
After finding no medical reason for the girls' illness, Samuel Parris tells the doctor that he suspects witchcraft because of the girls' involvement with the occult.
Step-by-step explanation:
After the doctor found no medical reason for the girls' illness, Samuel Parris tells the doctor that he suspects witchcraft. This is because the girls had been experimenting with the occult under the guidance of Tituba, a West Indian servant in the Parris household. The belief in witchcraft and the devil's influence was prevalent in Puritan society, and Parris attributed the girls' illness to supernatural forces.