If you fix the current applied, any additional series resistance (e.g. resistance of skin, which depends on which part of the body it is and whether you have a cut there) doesn't change the current that passes through the heart. What does change it is any additional parallel resistance, which is barely affected by things outside of skin (potentially modulo the case of the person being dripping wet with saltwater or similar, which _reduces_ the current that goes through heart compared to a dry person).
@robryk @freemo Valid points, assuming the poles are actually connected by the conductive liquid.
It can be seen as resistances in series and parallel to the current through the heart.
It remains that the path actually has to go through the heart or other sensitive organs - connecting shoulder and hand will hurt, probably do damage, but not kill directly.