How do you get an old pen to work?

19 December 2014
Presented by Chris Smith, Redi Tlhabi.

Why does scribbling on paper get a pen to work? Why can't mules reproduce? How soon will they be able to lessen the effects of Multiple Sclerosis? When you burn wood, where does the weight go? How do touch screens work? Plus, why feeling your age might be bad for you...

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