This rather fearsome bit of wood is called a trilla. We have two or three of them in the workshop at the back of the shop and I was cleaning them up ready for sale.
The shape is a bit like a sledge or sleigh - narrower at the front than the back and with the front part curved up slightly - like Ali Ba-Ba slippers. Underneath there are rows of sharp flints hammered into the wood and, on the newer ones, there were a couple of serrated metal runners too. On top there are lots of hooks and fastenings so that the sledge can be fastened behind a cow, ox, horse, mule or donkey and dragged round and round your wheat harvest to smash it up on a hard circular surface. A farm worker would sit on a chair placed on top of the trilla to add a bit of weight and to guide the animals.Once the harvest was cut into little bits it was thrown into the air. The light stalks blow away and the heavy seed falls to the ground.