A control is not necessarily an experiment. It is something to check the validity of an experiment with. Suppose you were testing to see if a certain chemical can make plants glow. Even if you made the plants glow, you haven't proved that it was the chemical which made it glow. The control proves, (or proves wrong depending on the result) that the plants glowed or didn't glow because of the chemical. The control would be to grow the plants without the chemical. If they glowed, then the chemical doesn't affect whether or not the plants glow. If they didn't glow, then the chemical is what makes them glow.