365 Days of Twinipedia - Day 25

Day Twenty-Five of Twinipedia: 

Fact #25

Conjoined twins occur in about every 1 out of 400,000 twin births. This event is rare but how exactly does it happen?

The informational graph below gives a great break down of how this occurs when the egg is splitting while forming the twins.

This great informational image is from http://en.rian.ru/infographics/20090918/156177591.html