[Pierre-Marie Baty]

@all: to cut this straight, it's a combination of both.

Huge amperages won't kill if there's little or no voltage.
Small amperages CAN kill if there's high voltage.

The amperage/voltage relation can be viewed this way:

Electricity is like water falling off a tap.
VOLTAGE is how high this tap is from the ground.
AMPERAGE is how much water gets out at once from the tap.

Now, the electrical conductivity is only determined by the orientation of the atoms (since electrical current is just a flow of electrons leaping from an atom to another). If the atoms are regularly aligned, like in iron and in most metals, the current will flow very fast. If that's not the case, this material will have much more resistance to current.

Water is another topic. The electrons in water and in liquids do not leap from one atom to another (since there's a HUGE gap between molecules in liquids), but instead they take one atom in hostage and form a ion. It's this ion (over-charged in e-, i.e. "overdepleted" atom) that serves the electron as an "embarcation" to cross the water.

Electrons, and through them, the movement of matter itself can be influenced a lot by Laplace forces, but that's also another (long) story.