Halve and seed the pomegranate, collecting any juice. Mix the juice reserved with the pomegranate juice and 200 ml (approximately 3/4 cup) of water and heat. Cut the lime in half, squeeze out the juice and add to the pomegranate juice.
Soften the gelatine in cold water. Squeeze and dissolve in the warm liquid. Pour in the grape juice and divide evenly among the glasses.
Pour in half of the pomegranate seeds and chill at least 3 hours cold. Before serving, garnish with the remaining seeds.