Bekhorot 55: The Jordan River and the Source of Blood

If the animals are grazing on different sides of the Jordan River, they cannot be combined for the purpose of tithing. Which leads the Gemara to a long detour of reflection on the Jordan River, including its role as a border (or not) for the land of Canaan. Also, the source of the Jordan - in the Cave of Pamyas, where an oath about the water at the source may well have impact on the permissibility about the entire rest of the river. Plus, the supposition that the source of blood is the liver (it's marrow, but it's true that the liver is home to more blood than other organs). And the source of water is the Euphrates.