I'm personally more of a science nerd so here's my take on it....
While a dead skeleton ceritanally could not bleed, a living one could. There are two types of bone marrow: Yellow and red. Yellow marrow is mostly made up of fat, while red marrow produces blood cells. In adults, red marrow is found in the skull, spine, humerus, femur, sternum, collar bone, and ribs. The latter two are located right where you hit Sans. Thus, the skeleton bleeds.

Or it could just be ketchup and I'm thinking too hard about this.

Still, the whole DT theroy's pretty good!

Interesting! Nice take on that ^^
Of course, knowing sans it most certainly could be ketchup >.<

Coolio.
Now, if only we could find out how he knows what a person looks like after they were killed 11 times in a row.

The fact that stuff can pop up randomly in zones and you can't see them until you bump into them

The fact that if you watch an ad you get a key or other reward. (??)

The fact that my Wii skier character crashed into walls and stuff and people a trilion times and...survived?

I read gaming

*ahem* Game logic:

animatronic can use pins to appear human and is actually a recreation of a man's daughter who later ate the child of a child killer and is now possessed with spirit of said child

but all this may or may not have canonically happened in the game

Just another dose of Pokemon logic:

-Everyone leaves their doors unlocked and just give you random stuff when you break into their house. Like Pokemon
-Adults are scared of team Rocket (And every other evil team) but they're constantly being beat up by 10-year olds.
-YOU CAN CARRY ANIMALS BIGGER THAN YOU IN A BALL SMALLER THAN YOUR HAND (Pokemon plz explain ;-;)
-The main character's expression almost never changes. It's weird.
-Nurse joy. (Joys?)
-The fact that you can have Pokemon in your backpack that weigh more than you.
-All those giant pokeballs you're lugging around in your backpack for when you find a dynmax Pokemon.
-How do escape ropes even work?

Aaaannnnddd I got nothing else.

If somebody already said something on this list and I missed it, please tell me!

The Joys reproduce via mitosis.

I dont know if this has been said but people just leaving money on the ground and also not caring weather or not you break their pots.(LOZ)

Being able to hold a lot of stuff, kill a dragon, break a tree with bare hands, killing cows with bare hands and then dying to hunger.
(Minecraft)

Edit: Every team rocket or team yell member looking the same