At the end of the episode 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 due to their body temperature being too low to sustain the virus.
When Alan is fixing a blown fuse at Lyndsey's house, he couldn't find a replacement fuse so he says you can replace it with a copper penny. This is true, although extremely dangerous and specifically with a copper penny as he mentions. Pennies went from copper to copper plated zinc in 1982 which can actually be melted by significant current. Alan didn't check the penny for a date before putting it in the fuse box though.