I had to twist this topic by Long and Short Reviews, because I honestly couldn't think of anything weird I had learned by reading fiction. I tend never to assume that weird things I read in fiction are true. So I came up with one weird thing from non-fiction and two from researching my own writing.
Otters play. I was a great lover of Gavin Maxwell's "Ring of Bright Water" and was fascinated to discover that otters are playful animals, spending hours tossing rocks around for sport. He also described that when playing fetch with an otter, it is the otter that throws the ball and the human who fetches it.
What happens if you squeeze a full can of drink. I had a scene in "The Hand He Dealt" with Ash squeezing his can of beer in shock and spraying it all over his girlfriend. My husband insisted the beer would simply run down the sides. So we filled a can with water, my husband stood in the shower and squeezed it. The resulting jet of water hit the ceiling, proving my point entirely.
You can pin someone to a tree with a spear. I haven't actually used this one yet, but my husband likes to remind me of it as a weird question I once asked him. Although apparently you'd be better using a pike. A spear is for throwing.
So what weird things have you learned while reading?