#2 - Those two are too stupid to comprehend.
More of those lovely homophones today- two, too and to. What's the difference?
Two - Simply the spelling of the number 2, e.g. 'Two plus two is four', 'Two nuns walk into a bar'.
Too - Is used when you are describing something that is to an excessive degree, over, or more than enough, e.g. 'There are too many stupid people in the world', 'Bill Gates has too much money', 'I've had too much wine'. It is also used in place of 'also' or 'likewise', e.g. 'Can I play too?', 'Is The Old Republic going to be awesome too?'
To - Used in all other cases, of which there are many. Just remember the rules above and if the context doesn't fit then it'll be 'to'.