Certain areas had a lot of candomble and macumba, which are the Brazilian versions of voodoo--practices that involve calling on, worshipping, making sacrifices to various spirits. We often heard the drums and chanting that was part of their rituals. And we often found in the streets what remained of animals they had sacrificed trying obtain a blessing or bring down a curse.
A few examples:
A kid we taught told us he had conducted some kind of occult ritual to "test" the Book of Mormon we left with him. (I was like, bro, the test was to read and pray!) He was super impressed by the "power" the book had displayed and said some other weird stuff about that. The spirit told us to take the book, get out, and never go back.
A woman we taught and baptized had gotten caught up in that stuff, very badly wanted out, and didn't know how to escape. We didn't fully understand the darkness it brought into her life at the time. A while after her baptism, she told us that she often had a recurring dream that she was falling deeper and deeper into a bottomless pit. And that one night, shortly before she met us, she dreamed that two angels flew into the pit after her and pulled her out. "You were those angels" she said to us. Honestly, I still get chills thinking about that.