Always watch out for mutants
Mutants are commonly encountered in Fallout. Some, like the shuffling, skeletal ghouls, are simply humans who got exposed to ridiculous amounts of radiation and transformed. The others – people that were subjected to the Forced Evolutionary Virus – are the ones you've got to worry about. These are the Super Mutants, and they're big, hulking green monsters who are impeccably well armed and always, always want to see you dead. Naturally you'll also see lots of mutated wildlife too - rats, scorpions and two-headed cows, among other beasts.