An individual migrates from body to body (usually when the going get's rough) by stabbing his/her/it's future host with a super duper hexed up knife. Once the transfer has been made, the wounds he/she/it inflicted heals and our body-jacker is back in business having escaped trouble and cheated death once again.
Interesting idea, I guess, though the execution could have been better. Notwithstanding, it's not a total waste of your time. I was conscious from beginning to end, so that's saying something. It made me think: What would I do if I had a knife like that? Would I use it? -Would you? These are deep questions, folks. Deep, troubling questions (Please keep a straight face). All you have to do when your body is no longer usable is stab the sh*t out of your fellow man or woman (Does it work with animals?) with your special knife and "Wallah!" -You have a new body.
The Ferryman may just boil down to personal taste which basically needs no rhyme or reason; you either like something, or you don't. I found the infatuation with the dog in the movie a bit annoying. I wanted to scream "Enough, already! -I know you love your little doggie, but give me a break!" If you had 10 mil, we know where it's going. -Sheesh! Guess I'm not a dog-person. Love, Boloxxxi.