"One of the most enigmatic images in the Nunnery Quadrangle is the stacks of doubleheaded serpents that form Vshaped designs above the outer doors. Perhaps the most interesting suggestion concerning the identification of this design came from ViolletleDuc, a nineteenthcentury French architect who wrote commentaries for Désiré Charnay's photographs. He suggested that the pattern represents wood cribbing.
We would like to go further and suggest that the design represents a corn crib for storing dry maize. In fact, the Yukatek of today call this kind of crib a kan che', or "snake wood". Each of the elements in the stack has a snake head on both ends. It is a kan che'. This idea seems particularly appropriate to the iconography of the neighboring South Building, which shows growing corn. The building itself may have been named for this crib, because a smaller version of it consisting of three levels surmounts the masks over the central door like a little billboard."
Schele & Mathews, The Code of Kings, p. 268