I'm looking at the table on http://www.allaboutcircuits.com/vol_1/chpt_3/4.html that describes the effect on the body of different levels of current, and I'm confused by the labelling. If the second level in the table is truly the "threshold of perception", how can there be a level below that? I'm taking "threshold of perception" at its literal meaning, which is "the lowest possible point at which current can be felt", so I don't understand how there can be a lower level than that. I should add that I know nothing whatsoever about electricity, and I'm copying this table into a course - just want to understand it myself before I expect anyone else to understand it.

 

Since the rest of the scale is pain related, I would have to reason that the perception threshold is that of pain.

Edit: Although, hyperphysics has 1mA listed as the threshold of perception and a slight tingling feeling...

Edit #2: The US government also lists 1mA as the threshold - methinks you found an eBook error...