America's number one source of litter? Cigarette butts. Around the world, some estimates say several trillion cigarette butts are littered each year. The trash ends up floating down drains and polluting water—and also as a sometimes-fatal snack for unsuspecting birds. The Filter Factory is a project designed to help remind smokers not to toss cigarettes on the street. Stubs in the vending machine are shredded up and turned into birdhouses as a statement about the effects on birds.