Quoted from a friend's mail
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"from: http://arivagam.blogspot.com/2006/11/wear-helmet.html
[ Ganesh was Parvathi's son (not shiva's). Oneday, Shiva cut ganesh's head with his trident, in an angry fight. Regretting his act, shiva ordered his followers to bring somebody's head to fix it over ganesh's torso.
"tharudhalaihalaa!! edhaavadhu oru thalai kondu vaangada. en pondaatti thalaiyai pidithu aattuhiral."
His wise(!!) followers brought an elephant's head. Ganesh survived after that skillful head transplantation by Dr. Shiva. MBBS, FRCS(Kailasam) ]
-Gokul"
