Quote from Phunkie;853708:
Pain isn't what kills you though.
This is what i've found
When a guy gets hit in the testicles, besides the agony from the glands themselves, the attack on this nerve centre causes the abdominal muscles to lock solid. This causes him to hunch forward, unable to straighten up for some time (therefore protecting the testicles from further harm) This also has the effect of squeezing the stomach, creating the feeling of nausea that guys get when this happens. And it interupts his breathing so that if the cause of the pain is prolonged(eg. the testicles are being squeezed) for more than 30secs or so, he will lose conciousness! And yes, in extreme cases it will actually stop the heart beating, resulting in death! [LEFT]
http://wiki.answers.com/Q/Can_you_die_from_a_hit_to_the_nuts#ixzz1tguscZVI
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