People may wash octopus with flour for a variety of reasons. One reason is that the flour can help to remove any slime or mucus from the surface of the octopus. This can make the octopus cleaner and more presentable.  Another reason is that the flour can help to tenderize the octopus meat. This is especially useful if the octopus is going to be cooked whole. Tenderizing the meat can make it more enjoyable to eat.  Washing the octopus with flour can also help to prevent the octopus from sticking to the cooking surface. This can make cooking easier and less likely to cause a mess.  Overall, there are a few reasons why washing octopus with flour can be beneficial.