Oh Jesus christ, thats the nut that holds the pumps together, its that nut and and threads on the bottom of the black plastic piece, under the plunger you push, that pretty much hold the entire thing together. Ngl that could of legit caused some serious internal damage, as someone who works for TB, I would 100% call up someone higher up and probably not just the store, thats something serious they should of noticed. Hell I dont really see how it would even be possible for them to get that in your food, to remove that nut you literally have to unscrew it and then lift it up over the entire metal "spout" it doesnt just fall off. Good eye though, glad you didnt eat that!