Mary then uses a metaphor to connect "birds of a feather" to the townwomen who are all standing beside each other, acting as though they are all the same. They "burn" collectively, which means they are all guilty of being inactive and failing to save Mary. This idea is expressed by using similar words in English and French to describe these women: they are "feathers" and "feuilles" which both mean leaf. Birds of a feather have been understood to mean people who share the same interests or hobbies for many centuries now. The first written record of this saying comes from 1598 but it may be much older than that. The original meaning was that if certain types of birds were found together in large numbers, there must be some kind of connection between them. For example, if we saw lots of parrots on a tree, we might wonder what type of bird was responsible for bringing them together. The expression "birds of a feather sit together on eggs" originally meant that pregnant women tended to associate with others also expecting babies. It's not known exactly when this phrase was created but it's thought to be around 1869. The common blackbird is the species used as an example in most cases where this phrase is applied. However many other kinds of birds are able to create their own nests so this statement should not be taken as evidence that all pregnant women will do something else together.