the reward system or canal in the brain, is a strange and interesting monster. But it is interesting never the less that the way we get high is 100% natural. Like it was always meant to be that way! My favorite analogy is for it is this: THC is like a key floating around in your blood stream. The receptors are like master locks. Only the key that is designed to fit into the lock will open it and unlock it. So here comes thc floating around bumping into all different kinds of locks, until BAM. It hits the one it was meant to unlock, the key fits into the lock, and they combine becoming one. Causing the reaction in the brain that causes euphoria.