This exercise involves "faces-and-vases" (an illusionary work), focusing on the feeling of the L-Mode shift to R-Mode in the brain.

The basic steps is make the first profile according to your dominant hand (right would do left face, left would do right face first).
Then labeling the parts of the face (forehead...nose...upper lip...lower lip...chin...neck).
Draw the parallel lines for the top and bottom.
Finish the vase/drawing.

When I was working on this I didn't feel that specific "crunch" of the shift. It was very fast with the start and parallel lines but it DID get a bit of a slog for the right face. I struggled with making the landmarks align up and redid some strokes until I just gave up with being satisfied. It felt like my usual process with art, parts where I'm familiar with go by fast but finer details or shapes I don't draw often tend to require a lot more trial and error in the roughs/sketching stages before being refined. I did however have to ignore the labels when continuing the piece since it was rather distracting.
Maybe that's it? I'm not quite sure, but actually writing how this feels is a bit odd for me. Maybe what I did notice holds more significance than what I am giving myself credit for. It's more abstract paying attention to internal workings, always worry I might be exaggerating or trying to fill gaps with labels or such which feels like I'm not observing "properly" or am making things up.