Who is kidding who? Just watch a film of a single cell critter, approach something and one , go yum! and engulf it or two go ahhhhhhhh!, and run away I believe the full technical explanation for that goes, mumble,mumble,chemical receptors something, mumble mumble.Humans are sensitive to certain chemicals in the parts per billion, and your finger can detect surface roughness down to 1/1000'th of an inch, thats the standard issue, exceptional indivuals with training will perform significantly better.