Its actually a bug in the engine with water in containers. Although graphically it looks like the water is inside, if you step in the water a ripple extends out the sides and over the ground. Throwing a bird into water will soften its fall so it isn't killed on impact so throwing it into a container will create a conflict. On the one hand it lands in water so it live, on the other hand it hits the sides so it dies, but again the water extends through the sides so it lives. This makes the chicken immortal and it will fly in a straight line until it hits an object because it will continue its conflicting movement by going straight (travel through water in container), bouce once (hit the side), then come to rest with its 'living animation' and movement (rest against oposite side while dead/alive).

I was actually was surprised by a guy who escaped my murderous rampage and I threw the chicken at him like a poultry missile. It flew straight at him, bounced off the wall behind him when he sidestepped, then killed him as it hit him from behind where it then proceeded to walk into the sky. Should've screenshotted it but that was what started the poultry gathering.