At the end when Alan and Walden are at the bar discussing their week of living with their girlfriends, Alan says he possibly has rabies from being attacked by a possum. Possums are immune to rabies because their body temperatures are too low to sustain the virus.
CORRECTION: Possums are absolutely NOT immune to rabies. They are just less likely to contract the disease.
CORRECTION: Possums are absolutely NOT immune to rabies. They are just less likely to contract the disease.
When Alan is fixing a blown fuse at Lyndsey's, he can't find a replacement and says he can replace it with a copper penny. This is true, but it's extremely dangerous, especially with a copper penny as he mentions. In 1982, pennies went from copper to copper-plated zinc, which can actually be melted by significant current, but Alan didn't check the penny for a date before putting it in the fusebox.