Decapitated Head Reacts Before Death

A few days ago, I thought if decapitation is the easiest way to die and pain-free at that. If the head is decapitated, will instant death follows?

Then an interesting article comes my way. There were times pala that decapitated heads still react to stimuli for a few seconds or so. Medyo nakakatakot kung mawi-witness mo 'yun, but then again, nakakalungkot din. Ano kaya ang tumatakbo sa isip ng ulo na 'yun? Ano kaya ang nararamdaman niya? Hay, basta nalungkot ako just thinking about it.