Nothing, they are free of charge.
Baby's because you can use a pitchfork
You use a cow-culator. Or you round them up. Or any other method the commenters want.
The police came and took statements but ultimately Mrs. Claus declined to press charges. OC
I feel positively charged!
A Li-ion battery.
Batteries have a positive side! inspired by: http://www.reddit.com/r/Jokes/comments/2zlrot/howmanyfeministsdoesittaketochangea/