Currently doing some beginner practice with Alexander Lenard's translation of Winnie the Poo. It says, "Ecce Eduardus Ursus scalis nunc tump-tump-tump occipite gradus pulsante post Christophorum Robinum descendens."

'Occipite' is in the imperative mood, but why? I don't see how the context calls for it. Any help is appreciated.