The download button opens the iTunes App Store, where you
may continue the download process. You must have iTunes installed with an
active iTunes account in order to download and install the software. This
download may not be available in some countries.
From Matt Martindale:
Make your friends laugh with "iFangs"!Scare your parents, put them on your dog, or use them in your next family portrait. With "iFangs", your imagination is the limit!Take your pick from one of the ten unique sets of monster teeth and place your iPhone or iPod touch to your mouth. Then let the laughing begin! iFangs will seamlessly loop until you're done scaring your friends. To go back to the main menu, simply shake your device.