The FAA teaches that the air wants to get from A to B over the top, at the same time as the flow goes underneath from the same points. Why? Does air have a mind? Does it have evil intent? is air sentient?
They don't teach this anymore, it's been corrected. But there are still stragglers, since it's so simple and elegant and ties everything together...
when the blade gets to the other end of the pond, stop the blade, and the point where the blade stops will generate another vortex off the leading edge... both the start and stop vortexes are opposite directions to the bound vortex that was developed by the flow around the spoon/knife, foil, cheese slice, etc.
The starting and stopping vortices are opposite to each other. The starting is CCW, stopping CW (stopping same as bound vortex). So all 4 vortices surrounding the rectangle swept by the wing's motion (starting, stopping, and 2 wingtip vortices), curl so the top goes inward, and the inside goes downward, which matches the downwash where the lift occurred.