Lie Detector

Jon, Jian and Ken are called upon to test a lie detector .

Jon says: “I think I can empty 20 bottles of beer”. BUZZZZZZ, goes the lie detector.
“Ok”, he says, “10 bottles”.
And the machine is silent.

Jian says: “I think I can eat 15 hamburgers”.
BUZZZZZZ, goes the lie detector.
“Allright, 8 hamburgers”.
And the machine’s silent.
Ken says:
“I think…”,
BUZZZZZZ goes the machine.