daf bit: Niddah 17

The rabbis are discussing bad traits and dangerous activities. R. Shimon b. Yochai said: the following things cause a man who does them to forfeit his life and his blood is upon his own head: eating peeled garlic, onions, or eggs or drinking diluted liquids, if any of them were kept overnight; spending a night in a graveyard; cutting his nails and throwing them away in a public thoroughfare (and some others). For the garlic etc, this is because an evil spirit might descend upon them, but it's ok if they're stored with their peels. The graveyard: because he might be exposed to danger. And the nails: because a pregnant woman passing over them would miscarry, but this applies only if he used scissors. (17a)

My edition doesn't further explain any of these. All cultures have superstitions; I guess these are some of the ones of this time.