I suspect many of you who watch the above video will know exactly how it's done but it's not immediately apparent to everyone, especially if you choose to present it in a way that isn't quite honest about what's going on.
I use this demo in my teaching to introduce the idea that an object will topple over if the line of action of its weight lies outside its base. I usually present it as a challenge: I start off with two identical (apparently) empty drink cans on my desk (yes, I know the ones in the video have slightly different designs). I offer one of the cans to a student and challenge him or her to balance it on the edge of the base. I tell them I'll try to do the same with the other can. I make a big show of concentrating, then reveal that I have managed to make my can balance while the student's can keeps falling over (this usually gets a gasp of approval -- as I think the video shows, the can balanced on its edge looks quite disconcerting). After the initial surprise at my being able to balance the can, the students usually guess that something's not quite right.
I think this demo works well presented as a "magic trick" because it provokes the question "what's going on?" or "how does that work?" and that's when the discussion begins...