More puns

Based on the other line of comments...
We don't.
Talk.
About the source of milk.
In the Underground.

Sans: Bro wdym??

Uhh, you alright there buddy? You look about as pale as milk right now.

Sans: *WHEEZES* I thought I lost my breath there, then I realized I don't even breathe.

So there's that brand-name chocolate bar in Toriel's fridge. Everyone knows there aren't any normal animals in the Underground, and Toriel doesn't rummage through the garbage heaps. How was it made?

Sans: Dunno

So, cows aren't the only animals that make milk.
There's the entirety of the mammalian species. One famous example being goats.

Sans: Your point??

Well, Toriel is a goat.

Sans: And??

Man, that skull is thick.
Nevermind-

JESUS

SANS YOU THICK SKULL HOW DO YOU NOT CONNECT THE DOTS TORIEL WAS MILKED!

Don't make me get Toriel here because you discriminated her species.

Sans: What did I do wrong??

Udder jokes? Really?

Sans: Is there anything wrong with cow jokes??

Toriel is close to a cow.

Sans: And??

JESUS CHRIST