One Little Character Makes All the Difference

I went out to dinner the other night with my Chinese friend who can’t speak English. I ordered a few of my favorite dishes and told him to choose some as well. But I had to be careful with him because he likes to eat very traditional foods, like intestines and feet.
“No feet! No heads! No intestines! No fish!” I said. He laughed and agreed. Then he pointed to a dish on the menu that said: 牛蛙 . (If you speak Chinese you know where this is heading.) I knew the word 牛 meant cow, or beef, but I didn’t recognize the second character.
“Niu wa,” my friend kept saying again and again, like if he repeated it enough I would finally get it. “Niu wa, niu wa, niu wa.” I knew it wasn’t intestines or brains or anything but there are a lot of internal organs of which I don’t know the chinese for so I asked him what part of the body it was.
“Legs,” he said slapping his own for effect. “Big Legs.”
Okay, cow leg meat? Sounds like I could live with that.
When the dish arrived, bubbling in a soup with veggies, I knew something was wrong. The meat was clearly not beef, and didn’t look at all like it could belong to any part of a cow. In fact, it looked more like fish, with grey skin peeling back and large pieces of bulbous white fatty meat.

“Is this fish?!” I asked him.
“No,” he said repeating the word again. “Niu wa.” He even slapped his leg again a few times. “Big leg!”
I said I didn’t understand. “Is it beef?” I asked more tentatively.
“Not beef,” he answered. Then in an effort to help me understand he made the noise of the animal, “Gwah-gwah!”
Unfortunately in China animals make different noises. Cows don’t moo, horses don’t neigh and sheep don’t say, baaah. Instead they have their own onimonopias. For instance when you want to imitate a dog in China you say wang wang, not ruff ruff or bark bark.
So I’m trying to figure out what animal makes a gwah-gwah type noise. “Duck?” I guess. He shakes his head no. I’m especially confused because the name of the dish clearly indicates it is a cow, or beef, but he’s telling me it’s not.
“Use your dictionary,” he finally says. Then it all makes sense.
Niu wa means: bullfrog.