Sentence:  Meanwhile Nanny Broome was recovering from her initial panic and seemed anxious to make up for any kudos she might have lost, by exerting her personality to the utmost. She took the policeman's helmet and placed it on a chair, and unfolded his tunic to <WSD>shake</WSD> it and fold it up again for him. 
Meaning of the word marked with <WSD> tags:  To cause (something) to move rapidly in opposite directions alternatingly.