And they went away one by one

Jesus bent down and wrote on the ground with his finger. The ground represents the human heart, which gives forth its fruit in good or bad actions; the finger, which is flexible because of the articulation of its parts, represents discretion. So the Lord is instructing us that when we see any faults in our neighbours we should not immediately and rashly condemn them, but when we have humbly searched our own hearts in the first place, we should examine the issues carefully with the finger of discretion.

Quote: Alcuin, quoted by Thomas Aquinas, Catena aurea on John 8, l. 1; trans. PAC.
Ill.: He Qi, The Woman Caught in Adultery (Asian Christian Art Association).