The name kingsnake reflects diet. Lampropeltis species are ophiophagous, meaning they eat other snakes, and rattlesnakes are regular prey across much of the California kingsnake's range. A rattlesnake that detects one often responds not by striking but by flattening against the ground and using a raised body loop to bat the attacker away.
Two traits make this possible. Kingsnake serum contains proteins that bind and inactivate the haemorrhagic components of viper venom, giving substantial resistance to a bite that would kill a comparable colubrid. Separately, comparative work has found that kingsnakes generate greater constriction pressure relative to body size than most other constrictors, which lets them subdue prey close to or exceeding their own mass.
Resistance is not immunity. It is partial, varies between populations, and is directed at the venoms of sympatric vipers rather than at venom in general. A kingsnake taken from one region does not necessarily resist the venom of a viper it never encounters.