Disposable Cup Dispenser Brown Residue At Bottom Of Disposable Plastic Cup?

Brown residue at bottom of disposable plastic cup? - disposable cup dispenser

Hello everyone,

This morning, I pour some water in one of those disposable plastic cup is red in the shop, then pour in a swing, and take, I looked and looked in the back was a brown stain - or at the bottom of the cup. I quickly threw the cup and took another.

But to my knowledge has been used, but may be wrong, but nobody knows what the hell was that? And what happens to me?