I'm ashamed to admit that I know this, but Candy Crush uses a similar method of doling out free lives/moves. If you give a bunch of friends free lives, they get

I'm ashamed to admit that I know this, but Candy Crush uses a similar method of doling out free lives/moves. If you give a bunch of friends free lives, they get asked to give you a free life in return. Always saying "yes" will indirectly get you more freebies in return.