Sentence:  He ran on his plump sticks of legs , freezing now and again into the <WSD>sudden</WSD> startled attitudes which the camera had caught and held on the paling photographs , all carefully placed and glued and labeled , resting in the fat plush album in the bottom drawer of the escritoire . 
Meaning of the word marked with <WSD> tags:  happening without warning or in a short space of time