A moulinet-like move on the left side, that ends with a descending cut. The sword starts on the left side and high. its tip then goes down and back in a circlular motion, that naturally continues up and results in a downwards cut. In I.33 durchtretten is always being done only on the left side.
Durchtretten is typically done as a response to the opponent's rebind. If the opponent pushes my sword down and to the left, I can yield under his presure (beginning of a moulinet), let him push through, and immediatelly return with a cut (end of moulinet).
Durchtretten can also be done from my initiative, without the pressure of the opponent that I could yield to. If our blades are crossed so that the opponent's blade is on the left side of my blade, the I can do my durchtretten. The beginning of the moulinet will push the opponent's blade down and to the left, thus creating a space in which the end of my moulinet can cut.