When it's under an upside-down box one mouth is going to feel the same as any other.
There is a certain traditional wedding game in Eastern Europe where a blindfolded groom gropes the legs of women in search for his wife; he wins if he can find his wife by touch alone. Imagine a similar game, but instead of blindfolding the groom we put all of the women in cardboard boxes, and then he just reaches with his hands underneath the box and gropes their mouths instlead of legs. Would you be able to tell one person from another just by touching their mouth?