I have used gut as a bow string. It was small intestine from a whitetail deer.
Slit it lengthwise. It will be in layers with a fatty layer in between each, peel them apart and scrape the fat off them. Hang them somewhere with a weight. When dry, and that depends on humidity, but is only a couple of hours in sunlight with a breeze, twist it before bringing it down.
It is hard and stays stiff but will soften up in the area where the bowman's knots are tied. It is not as flexible as a sinew string but is not as stiff as rawhide
If you have dogs, they love it and will chew on it every time you turn your back on them. And they will destroy the tip of the bow while they are at it.