It's not as obvious as it could be, because the images were taken from slightly different angles and with slightly different exposure settings, causing a lot of visual distraction.

I was able to clean up the animation a little bit: https://i.imgur.com/cgKSA7H.gif

I'm with you - I noticed that little pac-man, but it's not an optimal way to see the difference. Seems like scaling both images and doing an image diff would be much more effective. That's a standard tool in semiconductor manufacturing.

Look at about 8 o'clock roughly 2/3 of the way from the center to the edge.

Used SIFT and OpenCV to align the images a bit better: https://imgur.com/a/vGORFxX

I easily spotted the difference, but the article says “a black lentil in the lower left area has been removed”, and I couldn’t see the removal.

Maybe they meant “a black lentil in the lower left area has been moved, thereby moving another lentil a little bit”? (Seems an easier demonstration to me. Removing a single lentil is trickier than moving one a tiny bit)

Look at around 8.45-9pm (clock dial direction) in the photo, you should see it readily now.