Theo Anthony’s documentary essay is a mashup of topics designed to get viewers thinking about Baltimore, and what institutional systems, such as redlining, may have contributed to some of its current woes. And yes, there are rats — local Baltimore rats. Rats that were part of an influential Johns Hopkins study on slum life. Rats that bedevil current homeowners who just want to sit in their yards. And rats that have the misfortune to become the target of hobbyist rat-hunters, and a longtime city exterminator. There are also ruminations on virtual-reality depictions of Baltimore (marred by weird glitches); a visit to an extraordinary set of tiny crime-scene dioramas; and, for contrast to the inner-city rats, some “fancy rodents” who enjoy what amounts to run-of-the-house in the suburbs. There is some interesting material here, and occasionally the disparate pieces pair well to make significant connections. But elsewhere, the material feels too incongruous, and the film’s experimental exposition falls flat. But the garrulous city rat-catcher, with his understanding of (and respect for) how rats persevere, is never less than entertaining.