levo,
Any wing produces a trailing vortex ("wake turbulance") due to the spillage that creates a neat little sideways tornado at the tips. The blade is of course a wing, and it produces a tip vortex. Because the whole flow field around the rotor is downward, this tip vortex descends as it leaves the blade tip.
The vortices can be seen when you hover over grass, they make the rapid beating of the grass that marks each blade passage.
In level flight, as the rotor turns, the next blade avoids the previous blades vortex because the downward drift of the vortex causes the miss. If the rotor is tilted back a bit, as in a quick stop, the "next" blade can hit the vortex and cause a bit of vibration and a slight "slap".
The most famous bit of Blade Vortex Interference (BVI) is the Huey "blade slap" in gentle descents at about 80 knots. Often the noise during translational roughness is BVI.
The blade stresses are not terrible during BVI, usually high speed flight and maneuvering are much harder on the blades.
Here is a blade tip vortex photo.
Here is a rotor blade shedding its vortex periodically:
Here is a NASA photo of one vortex path:
