Short answers, pulled from the story.
A flail is a hand tool used for threshing, the process of separating grain from its husks. The user grips a long wooden handle and swings it so that the attached swingle strikes a pile of grain and knocks the husks loose.
Flails used in Quebec to process wheat typically had a handle about 1.5 metres long and 3 centimetres in diameter, joined to a second stick about 1 metre long and 3 centimetres in diameter with a slight taper toward the end.
One of the first recorded uses of a flail as a weapon was at the siege of Damietta in 1218 during the Fifth Crusade, as documented in the chronicle by Matthew Paris. Tradition holds that the man who wielded it was a Frisian named Hayo of Wolvega.
The flail is proposed as one of the origins of the nunchaku, the two-piece weapon in the Okinawan kobudō martial tradition. Both share the same basic design of two rigid sections joined by a flexible link.
In ancient Egypt, the flail was a symbol associated with the pharaoh and was said to represent the monarch's ability to provide for the people. Pharaohs were depicted holding both the crook and the flail together, though what the implement in the artwork actually was remains uncertain.
A mine flail is a vehicle-mounted device used for demining. It uses heavy chains ending in fist-sized steel balls, attached to a rapidly rotating rotor, to pound the ground and detonate buried land mines safely before the vehicle passes over them.