I just got caught phoning Jo across the office. I couldn't see her to ask her a question as there was a queue of students so I phoned her desk.

The queue slowly became aware that we were talking to one another and we got very embarassed.

We were testing cartesian skepticism - "if you can't see me I don't exist".

So there.

I used the phrase "The girl with the blonde hair is onto us" and we hung up quickly.