if its just the two of you, it will often go without comment or notice. but if there is anyone else there and they are also picking up the lie vibe you will instantly be rewarded with a huge smile and make a great new friend
you have to say the 'i believe it' part in a tone that conveys that the evidence of the lie being true is the you believing it part, and that there is no additional evidence worth considering. *i* believe it, therefore it must be true.
@doot this just reminded me of the time when academy award nominated actor josh brolin sunburned his asshole