A neat trick to do with an empty or nearly empty soda can.
Step 1: Meterials
You'll need to obtain an empty soda can(Oh, goodie! caffinated goodness!), and about 70 mL of water. The amount doesn't have to be exact, but it has to fill about 1/5 of the can.
Step 2: The Only Step
This is be no means a complicated trick, just dirnk all but 1/5 of the soda, or take an empty can and fill it a 1/5 of the way. 1/5 works the best, Beleive me, I've performed this trick in planes and got the best results from 1/5 full.