After a parade of stories about people bringing exotic animals on board planes for emotional support (and some airlines tightening rules on certain pets), the Department of Transportation has stepped in with a list of what is—and isn’t—officially allowed on board.

The DOT’s Enforcement Office has issued a comprehensive guidance report on the transportation of service animals, clearing the way for people to bring miniature horses onto planes, as well as pit bulls and any other dog breed and cats.

As for animals like birds? Those are a bit of a gray area. The DOT said airlines are subject to potential enforcement action if they categorically refuse to transport other animals.

However, the office said, airlines are welcome to continue denying transport to snakes (news that’s likely to cheer Samuel L. Jackson), other reptiles, ferrets, rodents, and spiders.

Passengers will be allowed to bring up to three animals on board, said the DOT, even on flights that last longer than eight hours. Only one of those, however, can be a support animal.

The ruling is not law, but the department says airlines that do not comply will be subject to penalties.

Horses might seem the odd part of this rule, but miniature horses have been used as emotional support animals for a while (and are largely allowed on planes already). Last year, however, Delta Air Lines banned pit bull-type dogs from its cabins on domestic flights after two employees were bit by a dog that was labeled as an emotional support animal.

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