http://sciencenordic.com/why-do-headless-chickens-run

Why a turtle can swim without a head
To understand Lindén’s research, we’ll go back to the chicken and the turtle:

The turtle frequently uses swimming movements, so it makes sense for it to have a neural network in the spinal cord pre-programmed to perform swimming movements when the nerve cells are stimulated.

This means that the nerve cells do not need specific signals from the brain to prompt a coordinated activation of the muscles required to perform a swimming stroke.


The turtle’s spine is a bit like the human brain in certain respects, but it is a much easier organ to work with. This makes it a good model for the nervous system and for nerve cells in general.
As long as the neural network is generally stimulated for movement, it is already pre-programmed to activate some specific muscles to perform the swimming strokes in coordination.

This makes it much simpler and easier for the brain to send movement impulses down the spinal cord.

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If a Rabbit has running or jumping movements pre programmed in its neural network and the brain is stopping it running and jumping , when it has no brain there is nothing to stop the pre programmed movements . so they jump and "run" when the brain is destroyed