Mentos & Diet Coke - check out the height on that rocket. Don't know if it makes a difference, but we used Diet Coke with Lime. How we did it: Take 2 Mentos, chew up one, stick the other to it and stick them both to the inside of the cap of a 2 liter Diet Coke bottle- leave enough room to close the cap. Secure the cap, and make sure the non-chewed one drops in. www.shiftdelete.com