Sheldon:  Do you want to hear an interesting thing about stairs ?
Leonard: Not really .
Sheldon: If the height of a single step is off by as little as two millimeters , most people will trip .
Leonard: I do n't care . Two milli - that does n't seem right .
Sheldon: It 's true - I did a series of experiments when I was _ twelve _ . My father broke his clavicle .
Leonard: Is that why they sent you to boarding school ?
Sheldon: No - that was the result of my work with lasers .