Thanks! As for the cow and leather mechanic, I agree they're in a bit of an awkward spot right now (wood too). Cow spawns are triggered when you return to the surface, and wood spawns are tied to the number of cells dug. The main reason for this setup is that both resources need to appear on the surface, which can be tricky in a digging-focused game.
I've always wanted to revisit how cows spawn and even considered removing leather entirely, but since it's such an important crafting material, that wouldn't really make sense.
I'm definitely open to suggestions for better ways to handle cow spawns, and if a good idea comes up, I'd be happy to change it :)