I read once that the noises that slot machines make, and more recently mobile games like candy crush etc are the truly addictive element. Its like when you use

I read once that the noises that slot machines make, and more recently mobile games like candy crush etc are the truly addictive element. Its like when you use a clicker to train a dog. Do the trick - hear the click - and get a treat. Eventually you don't get the treat anymore more, but that doesnt stop you doing the trick (putting another coin in the slot).