This morning, my sister posted on FB that the half-moon under your fingernail is an air pocket, and nobody knows why. 
Just like a duck’s quack doesn’t echo, and nobody knows why. :rolleyes:
Yep, despite having the entirety of Teh Intrarwebs at our fingertips, and nobody knows why a lot of things are. Yeah.
So let’s have a go at it - share your observations, factoids, speculations, or other absurdities, making sure they all end with: and nobody knows why.
nm
You can balance an egg on its end any day of the year, eclipse or not – and nobody knows why!
Thirty days hath September, April, June and November;
All the rest have thirty-one, except February, which follows its own weird rules* – and nobody knows why!*
When one of my ear-buds fails it’s always the right side one.
And nobody knows why!
Credulous people believe ridiculous shit they are told or read … and nobody knows why!
The Cheerios effect (two Cheerios in a bowl of milk will always end up together!), - and nobody knows why!
A few grapes can cause organ failure in dogs - and nobody knows why!
From Snopes:
“Ours is one of the virtual doors that gets knocked on quite frequently by these scavengers, and while we’re glad to help, our job is never done because anyone can make up lists like these: just invent four or five of the most far-fetched statements you can imagine, and follow them with the phrase ‘and no one knows why.’”
In total darkness, the kind only accessible in caves deep underground, the human eye can see significantly better than in normal darkness . . . and nobody knows why.
When you drop a piece of toast, it always lands spreading-side down . . . and nobody knows why.
Last night I dreamed our alphabet had no letter between “x” and “z”…and nobody knows “y.”
And no one knows why.
Your turkey’s meat thermometer pops up every time your wife opens the oven* . . . and nobody knows why.*
Seals are raping penguins, and nobody knows why.
When I grab a bowl of Wheat Thins, I eat them 2 at a time, and always end up with a single Wheat Thin. NKW!
The Lion’s have trouble attacking, and no one knows why.
People misuse the apostrophe, and no one knows why.
Bees can fly, and no one knows why!
“The Blair Witch Project” made $248,639,099…and nobody knows why!
Due to their aerodynamics, bumble bees can’t fly, but they do it anyway, because they don’t know why!
The spider lives in your right ear pushes it out. (It hates your music)
But nobody knows why it hates your music.