Evil Spirits

From the FIGU Forum (Questions Answered by Billy):

[In] the TJ there are many places [that] mention "evil spirits".

One significant event was in Chapter 8 "The healing of two possessed people".

8/32 Then the evil spirits in the possessed asked him, "Master, please drive us out, so that we may go into the herd of swine grazing just over there"........ the whole herd rushed down to the water and drowned.

What was really happened in that event? [Are] there any scientific explanation?

ANSWER: "Evil spirits" means negative psychic conditions.[1]