The clipping soldier is a glitch in Assassin's Creed III.
What Happens
In this glitch, a soldier or either redcoat or rebel orientation dies and subsequently his body clips through itself, creating bizarre and disturbing contortions like the one seen to the right.
How to Trigger Glitch
This glitch happens randomly when killing soldiers. It can be rare, but is also known to occur one after the other when it does rear its head.