Theoretically it wouldn't do anything - you are right there. However, of the three holes, one (the round one) is a true ground, and NOTHING can happen there. One flat one is "neutral" return, and in many North American systems this line is grounded back at the power supply transformer, so it has relatively low voltage on it at the outlet. But you cannot bet your life on that! The dangerous one is "hot", the other flat slot. If you push the paper clip in there AND if you were perfectly insulated yourself, there would be no circuit and no current flow. BUT usually there is some high-resistance connection from your body to ground and you could get a bad jolt. In practice, some older electricians used to make use of this - I've even done this myself - to test exposed wires to find the "hot" lead. Make sure you're NOT grounded as best you can, then "swat" your finger over the exposed wire, not trying to keep contact - only touch and brush past. If you feel the jolt of electricity, you found the hot lead! If not, your might risk trying again. Or, if you get a BIG jolt, you have BIG trouble! Not really recommended. But it does illustrate that you can get a shock even though you might think you have not made a complete circuit.