Has anyone ever wondered why there is any need for the litter caused by packaging from snack foods? Consider this: is a crisp packet easier to carry when it is full or when it is empty? Logic would suggest that an empty packet is lighter than a full one - even given that the mass of crisps is around 25g, or 1oz in English. If that is true, why is it so much more difficult to carry when empty? Why must it be dropped on the ground? Is not the pocket, rucksack etc. that held it when full not adequate to the task of holding it when empty? Behavioural psycologists might want to tell us that the person has no incentive for holding on to the package once the contents has been consumed; that, like a one-night stand, once gratification is complete the object can be discarded. I suspect that there is a reason far more weird than this: I suspect that something unusual happens to the gravitational forces within the empty packet, causing it to become massively heavy as soon as it is empty.