The simplest answer I can think of to the original question is as the aircraft slows, the Angle of Attack (A of A) increases and the center of pressure (C of P) moves. The aircraft slows and the elevator and stabiliser have changed shape (due to up elevator - back pressure on controls), producing negative lift so that the tail drops and the nose pitches up as aircraft pitches around lateral axis. As the aircraft slows this A of A increases more and more until the stall occurs.
While the wing and elevator/stabiliser continue to produce lift this works, the aircraft continues to fly in a nose high attitude. The aircraft continues to seem to fly normal, even though it may actually begin descending due to lift and thrust being less than weight and drag....ie total reaction formula....Some aircraft will descend all the way to the ground without snapping forward. Others will snap on or after stall as described below.
Eventually the aircraft exceeds A of A to point where wing rapidly develops turbulent airflow, produces significantly less lift and significantly more drag at the same time.....total reaction, significantly changes for the worst. Thrust and weight stay the same, but lift significantly drops at the same time as drag significantly increases.
The aircraft which was being held in an artificially nose high position from pilot input, reacts, with both a drop due to aircraft now in descent and a nose drop as aircraft rotates around lateral axis .... this combination of a loss of lift at the front of the aircraft, and a rotation is what gives the snap some describe at stall or shortly after.... for the most part its the rotation that the pilot notices most and describes as the snap. Its possibly the only time a beginning or non aerobatic pilot will experience a sudden rotation around the lateral axis other than a landing as they stall it on.
It is, just like when you hold a kids swing up and let it go, it drops around the axis suddenly, when the force holding it up is released suddenly.
The rotation can be exaggerated if the pilot simultaneously releases the back pressure and the "rear wing " (elevator and stabiliser) goes from producing negative lift to neutral, or positive for a moment due to its A of A.
Far from a perfect answer, but good enough to help, in some basic language i hope...