All of them have been cut in half with some sort of filling added - cottage cheese, meat, pickle, etc.
And all of them have been made in the same toroidal shape. Which has a hole in the middle, which lets bits of the filling fall out fairly easily.
Is it possible to make them without the hole? I presume that there's a traditional element, e.g. everyone expects them to be that shape, but is there any more practical reason, e.g. the flavour is different if there's no hole / the way that they're made only works for that shape? Has anyone ever tried to sell bagels that are a solid oblate spherical shape, like other rolls?
No particular reason for asking, apart from eating a cottage cheese bagel for supper, but now that I've thought of this I really want to know the answer...