1. The grey goo is a scenario that happens in some "worlds", which causes thwe world to end. What happens is a mutation in a nanomachine causing robots to self replicate and wipe out all human existence. I visted the sites...
http://en.wikipedia.org/wiki/Grey_goo
http://www.kurzweilai.net/meme/frame.html?main=/articles/art0142.html?
http://www.greygoo.org/

2. You should put acid into food which the robots love to eat. The robots will be attracted to this delicous food, but wont know what is in it. This acid will break down the metal they are made of and kill them. We should use an acid which will dissolve the metal and then you then dont have to clean it up.

3. Self Replication and cloning are the same if you look at it as producing the same objects. It is also the same because the grey good with self replicating robots will take over the world and if someone cloned themselves over and over they would probably take over the wordl as well. The only difference might be that the person cloning might not kill the human population but instead control all living things. Grey goo is more threatening to the planet because it will kill us all. Cloning will probably just result in a "govermental take over." Self replicating is also more dangerous because it is uncontrolable while cloning is controlable.