Some random events have options that allow you to "Sacrifice to X". For example a two-headed calf is born and you get options to Uralda (the cow godess) or Sacrifice to Urox (the anti-chaos god).

If yousselect this option, what does it cost you? Goods, cattle,magic? Or do these options cost nothing and all they affect is the consequences you get?

Never mind, I tried it and found out after you select the option you get another window to choose how much to sacrifice.
This was a stupid question.