I understand why sticking a knife into a toaster produces an explosive phenomenon. It completes the conductive connection between the two holes in the electrical outlet and the 250 volts or so that separate them cause a substantial current to rush through an almost 0 resitance. In other words the knife creates a short circuit.
But I don't understand why the person would get a shock. To simplify the problem we may as well assume that the person is holding a piece of aluminium with two branches, one in each hole in the outlet.
At any given moment, the voltage between each outlet hole and the earth is presumably at most something of the same order of magnitude as the tension between the two outlet holes. So the current will travel through both possible paths with currents inversely proportional to the resistances, that is, 300-1000 Ohms for the human body and some $10^{-7}$ or $10^{-8}$ Ohms for the aluminium, so basically the current travelling through the person to the ground shouldn't be of any significance should it ?
If the piece of aluminium only sticks into one hole then entire current flows through the person but if is sticks into both it doesn't.
