It's not his reaction which is funny. It's the marvel and discovery of her interaction with it. Her last statement is funny too.
I assumed she was just playing dumb for the video.
Haha, that end comment is funny.
Very likely not. There's lot of videos of younger people playing around with older technology. Technology has changed so much it's nearly a complete mystery to them of how it works. Things are so much easier and simple these days, the older stuff is completely non-obvious. That's the point of the guy's prompting. He's trying to drag out of her, her perceptions and how it works. That's why it's funny.
Now when they hear the clicks and realize how it's working.
As a bonus they could have dialed without the rotary element, just using the hangup button with their gamer reflexes.
(post is archived)