Calvin is a true believer from the get go, having watched his Marine buddies get killed and being left for dead himself. You can hack them, bash them in the head with a rock, even unload a rifle into them - to no effect. Lucky for our heroes they find this out pretty early on, but they never discard their rifles. The Los Angeles Airport has come a long way in forty years. Fog is caused by a race of slime people who have been forced from their subterranean homes by nuclear tests.
Slime people are scared of fire extinguishers.
Girls never said no to men's advances in the good old days. It's hard to take some guy seriously when he is holding a goat. The leading cause of breakins is authors looking for typewriters. Meat freezers have locks on the inside of the doors. Humans can see better than slime people, even in the latter's home domain of thick fog.