Students will need to allow access to the computer's camera in order for the project to work. Then, they can literally swipe their hands in the air to pop the bubbles!
A really nice feature of this particular project is the notes attached to the blocks explaining their function.
I also found this Video Sensing Studio on Scratch featuring several fun projects!
Check out this Scratch Wiki page for more info on Video Sensing blocks!
I'm sure your students aren't the only ones who will be having fun with this! ;)