 Newell later commented that he was impressed with the DigiPen team as "they had actually carried the concept through", already having included the interaction between portals and physics, completing most of the work that Valve would have had to commit on their own.Certain elements have been retained from "Narbacular Drop", such as the system of identifying the two unique portal endpoints with the colors orange and blue.A key difference in the signature portal mechanic between the two games, however, is that "Portal"s portal gun cannot create a portal through an existing portal unlike in "Narbacular Drop".