I was recently asked by a friend to check their back for a possible tick. I saw a tiny round dot without legs and said I think this is a scab. It came off easily. But they said there was no reason for them to have a scab back there, so I put the dot under a digital microscope, which showed that the reason there were no apparent legs was that the legs were curled up under the body:
And the reason it was round was that... there was no head.
So the microscope goes back on my friend's back and sure enough - there was the head - still embedded in the skin. There followed a prolonged debridement with available tools - a needle and alcohol wipes - with eventually satisfactory results.
The diameter was only about 3-4 mm, so this was probably a nymph. The attachment had been only for a matter of hours, so the risk of Lyme was negligible. Still it was a bit unsettling...