Evidence

Possession: As a Spirit, Petelgeuse can possess others' bodies, with Subaru describing it as a forcible one way contract. Compatibility varies between people, as he mentioned that Subaru's body was optimal while Ferris and Wilhelm's bodies were incompatible for various reasons. To make other people into his fingers, he adds a magic to their body that seemingly makes them compatible, so it can be assumed that he can possess people with the witch's scent but needs to make normal people into his fingers first. He used this over and over to live for 402 years until he was killed at the end of Arc 3.

Source: WN