Abominable to Egyptians

Moses tells Pharaoh that Israel has to leave Egypt to perform their sacrifice before Yahweh because what they intend to do is abominable to the Egyptians.

Why would it be abominable?

For starters, bulls were divine – or at least mediated gods – to the Egyptians. Not appropriate for slaughter.

Equally important is the fact that Egyptians rarely burned animals in worship anyway. (Neither did Mesopotamians.) They mainly burned animals that represented chthonic powers, and the burning was a sign of victory. To burn up a bull would be, well, an abomination. 

It seems that the Egyptians did not place nearly the emphasis on blood that Israel did, and they might have found the free spattering of blood offensive.

This leads to a larger hypothesis/suspicion: Sacrifice is often said to be the universal of ancient religion. I have said it. Provided “sacrifice” is understood as offering to the gods, whether or not it involves an animal and whether or not it involves fire, this is a factual statement. 

When we define of sacrifice in biblical terms as the slaughter, blood-spattering, and burning, then it is not true that sacrifice is universal. 

What is more nearly universal is what the text of Exodus highlights: Notions and practices regarding purity, pollution, and abomination.