Though no longer attached to the hand, it still holds its adversary in its grasp.

Dragon's Claw

Whenever a player casts a red spell, you may gain 1 life.

"If there is a fire that never ceases to burn, it surely lies in the maw of a dragon."
—Sarkhan Vol

Magic 2012

Duel Decks: Knights vs. Dragons

Salvat 2011

Magic 2011

Duels of the Planeswalkers

If a player casts a red spell, Dragon’s Claw’s ability triggers and is put on the stack on top of that spell. Dragon’s Claw’s ability will resolve (causing you to gain 1 life) before the spell does.

The ability triggers whenever any player, not just you, casts a red spell.