Stephen Morris of the University of Toronto presents this short video on the physics of dominos falling.
A domino can knock over another domino about 50% larger than itself. A chain of dominos of increasing size makes a kind of mechanical chain reaction that starts with a tiny push and knocks down an impressively large domino.
Original idea by Lorne Whitehead, American Journal of Physics, Vol. 51, page 182 (1983).
Yes, this is referencing a real paper published in a real journal.
(Source: http://www.youtube.com/)