When next you shoehorn yourself into one of America’s ever-shrinking airline seats, you might encounter a new wrinkle in the romance of air travel. You might be amused, or not, to discover a midsize — say, seven feet long — boa constrictor named Oscar coiled contentedly, or so you hope, in the seat next to you. Oscar is an “emotional-support animal.” He belongs to the person in the seat on the other side of him, and he is a manifestation of a new item, or the metastasizing of an old item, on America’s menu of rights. Fortunately, the federal government is on the case, so you can relax and enjoy the flight.

The rapid recent increase of emotional-support animals in airplane cabins is an unanticipated consequence of a federal law passed with the best of intentions, none of which pertained to Dexter the peacock, more about whom anon. In 2013, the Department of Housing and Urban Development told providers of public housing that the Americans With Disabilities Act of 1990 (ADA) mandates “reasonable accommodations” for people who require “assistance animals.”

The Air Carrier Access Act of 1986 allows access to animals trained to provide emotional support. Federal guidelines say airlines must allow even emotional-support animals that have a potential to “offend or annoy” passengers, but that airlines are allowed to — let us not sugarcoat this — discriminate against some “unusual” animals.