The Fly (1986).

I watched it only once, in the 90s, and I’ve never been able to watch it again since. At the same time, I think it’s an excellent film.

The seemingly light and even humorous beginning of the film is gradually replaced by the sheer horror of the gradual loss of humanity and the final transformation into a monster. Simultaneously, in my perception, a glimmer of hope for a good ending is created, only to be ruthlessly destroyed at the very end. Even the music from this film feels overwhelming to me.

I highly recommend it, but you should never watch it ;)