Well, about 1-2% of people have a peanut allergy, which is serious. For them, a peanut is less of a snack and more of a biological weapon. So always check before you share your trail mix.
Also, peanuts can sometimes grow a mold that produces aflatoxins. But don’t panic—commercial peanuts are tested and roasted to kill most of that. It’s like the FDA is the peanut police, and they’re on the case.