I know UTY isn't canon, that's why I said "if." But who's to say that they don't have some sort of plant for plant-based foods or other animals? Tricky Tony himself said this during the 10th anniversary livestream: "It never wasn't there, [and it] will never not be there. Every monster has to have a place to go home to. Every monster has to have friends; they have to have something to eat, somewhere to go hang out. The Underground is a wide place. The only limit to all of this is your imagination. My goal with these days wasn't to show you a new hidden truth that you will never be able to access... my goal is to remind you that you have always been able to go, if you just hold the key to asking 'What's there? What's under the bridge? What's beyond the horizon?' Maybe you guys feel only my answers to these questions counts or matters, but to me, I only feel the opposite. This is just one interpretation. The Underground is as big as you want it to be, and I invite you to come behind the wall with me." So it's perfectly plausible for either of us to be correct.
