What can I teach to non-maths major undergraduates in a $10$ minutes session? I will be giving a $10$ minutes teaching session and my audience consists of five to six possibly non-maths major first year undergraduates in Asia. 
I am free to choose any topic for the session as long as it can be understood within $10$ minutes. 
I would like to teach something that will interest almost everyone. For example, we use online transaction everyday so it might be of interest to everyone to understand underlying mechanism, that is, encryption and decryption. 
However, to understand it, one needs to understand linear congruences, which I think some of my audience might not have it. 

Question: What topics in Mathematics will be of interest to every undergraduate, including non-Maths major?

As I need to write teaching aim and learning outcomes as well, the topic cannot be a puzzle like Knights and Knaves as I am not able to suggest possible learning outcomes in solving the puzzles. 
I thought of teaching optimisation calculus in one variable without any constraint. However, I am afraid that I may spend too much time in explaining what is a first and second derivative.

In ten minutes you can't do too much.  I would try to explain something puzzling - like why 1 = .9999.... 
A related idea might be on the difference between a countably infinite set vs. the power of the continuum.  Cantor's diagonalization is easy to comprehend and provides a compelling - but curious - result.
