Props: Two limes, red ink, surgical syringe.
MAGIC:
This is a favourite old trick of black magic practitioners, who exploit the innocent rural people. Normally, villagers shun doctors and consult the Manteika, the witchcraft practitioner, when they fall sick. The Mantrika gives them an ordinary lime and asks them to cut it. When they cut it they find blood to their surprise, instead of lime juice, which frightens them. The Mantrika collects his fees witha promise to cure them and goes into his room, chants some (false) mantras and comes out with a fresh lime. The villager again cuts the lime and finds only pure juice. The Mantrika then says that the curse is removed.
SECRET:
The secret is very simple. The first lime is a prepared one. Take red ink in a surgical syringe and inject it into the lime. This can not be noticed. The second one is, of course, an ordinary one. The rest depends upon the action of the programmer.