In an attempt to convey a sense of urgency, the visitor kept staring at the man on the phone but soon noticed that he wasn't actually saying anything.
As the minutes passed, the visitor kept looking, nodding and pointing to his watch, but the guy inside paid no attention and just stood there with the phone in his hand, saying nothing into the receiver.
After a quarter of an hour, the guy inside had still not said a word into the phone. Thinking that he was being deliberately obstructive and just wasting time, the visitor finally lost his cool. Opening the door of the box, he tried to snatch the phone from the other man's hand.
"Do you mind!" said the guy with the phone.
Spoiler:
