I’m not sure about the following point, as it deals with the little details around the blue part of Jesus’ outfit. Blue parts in Giotto’s picture are forming a zone of uncertainty, as the blue colour didn’t survive the centuries very much.
When flopping the picture upside down, you may find a threatening face profile. Located near Jesus’ legs, the face threatens to those whom send Jesus to his death. Among them, you can see a guy forcing Jesus with a stick:
The faces threatens these people as if it says “you shall pay for that!” –