What is meant by "possessed by spirits" in Buddhism?

In this answer there is a quote from The Buddhist Monastic Code 1 - The Patimokkha Rules Translated and Explained by Thanissaro Bhikkhu, which reads in part > only when one is possessed by non-human beings In that book there are several references to being possessed by spirits or non-human beings, such as this from page 44. >State of mind. The bhikkhu must be in his right mind. Any statement he makes while insane, delirious with pain, or possessed by spirits does not count. My question is, **who or what is doing the possessing**? Is there a belief in Buddhism that some being (a hungry ghost or something else?) would actually take over the mind of a human? Is that type of cross realm interaction possible? How literally is possession by spirits to be understood? Thank you.