Possible Duplicate:
Why Couldn't Harry Destroy the Horcruxes With His Bare Hands?
In PS, Harry's touch damages and nearly destroys Quirrell because he is a Horcrux of Voldemort.
Why doesn't Harry's touch have the same effect on other Horcruxes? (Diary, locket, cup, Nagini)?
I'd strongly prefer canonical answers.
Please note that the obvious answers don't seem work:
Inanimate vs animate (Nagini is animate)
Made before Harry's protection by Lily was in place (Nagini was made after)
Made after Voldemort got new body with Harry's blood (doesn't make sense anyway, bu Nagini works as counter-example)
NOTE: Please note that Harry explicitly did touch Nagini (in DH), therefore the accepted answer by Kevin to Slytherincess' question that this is a duplicate of seems wrong since Kevin's answer seems to explicitly ignore Nagini.