I sometimes purchase whole calf liver or whole pork liver.
I look at the bile ducts inside the liver.
250 kg calf, may have bile ducts measuring 1 - 15 mm in diameter.
100 kg pig, may have bile ducts measuring 1 - 10 mm in diameter.
Those ducts do not stretch.
They are very tough and very hard, and almost impossible to stretch.
They are almost impossible to chew, almost as tire rubber.
You will have to chew bile ducts for more than 100 times to break it down with your teeth, they are so though.
Why are they so tough ?
Why inside liver?
I guess it is because they are suppose to hold bile.
There is no way you could push a golf ball size anything through those ducts.
Even trying to push smooth marble through those ducts seems impossible.
Think about that!
These animals are not very much different than we humans.
Cows also get gallstones.
Musk deer too.
Some animals don't even have gallbladder.
Horses don't have gallbladder but have the liver and the bile ducts.
Whales, elephants and rats have no gallbladder.
All members of the deer family except for the musk deer, all of the equine family (including zebras), camels, giraffes, elephants, rhinoceroses, whales, some birds (such as doves), rats and some fish do not have gallbladders.