What did the duck say at the end of his meal at the restaurant when the waiter brought him the check?

Question

Chetan was having a cup of tea in a restaurant when he called the waiter and told him that there was fly in his tea. Startled, the waiter took the cup and brought a fresh cup of tea. Moments later, Chetan called the waiter again and told him that it was the same cup of tea.

How did he come to know ?

Answer 1

I already have a bill