(NEXSTAR) — It may not seem like it, but there are certain words and phrases that cannot, in fact, be incorporated into a racehorse’s name.

The 2021 Kentucky Derby is just around the bend, and with it comes a crop of curiously named contenders, including Super Stock, Helium, and the delicious-sounding Soup and Sandwich. In years past, other competitors in the Run for the Roses have boasted such names as Shut Up (1944), Dunce (1959) and even Degenerate Jon (1980).

But believe it or not, these names weren’t chosen at random. Rather, the opposite is often true.

Owners who wish to register their foals for racing must first meet the strict criteria of The Jockey Club, the official registry for all thoroughbred horses in the U.S. (including Puerto Rico) and Canada. As per the organization’s naming rules, owners are prohibited from using anything that falls into 17 different “classes of names,” including those used by notable past champions or award-winners, or those used by other horses that are actively involved in racing or breeding.

The lengthy registry rules also dictate which names are — and aren’t — acceptable in terms of length, fairness and decency.

For instance, owners are prohibited from submitting any names that consist of more than 18 characters (spaces and punctuation included) or any names that include the terms “filly,” “colt,” “stallion,” or any other “horse-related terms.”

Also prohibited are “names that are suggestive or have a vulgar or obscene meaning,” including any name The Jockey Club deems “in poor taste” or otherwise offensive. But that doesn’t mean that some haven’t slipped under the radar: The Jockey Club has previously approved risqué names such as “Panty Raid,” “Strip Tease” and even “Sexy Bikini Model,” according to its own database.

Another rule stipulates that horses cannot be named after any “living persons” unless The Jockey Club is provided with written permission from the namesake. It’s happened many times over the years, but one of the most notable instances occurred when Barbara Bush — who was first lady at the time — gave her written consent for a filly to use her name, according to Jockey Club registrar Rick Bailey, who recounted the story in a 2005 interview with NPR.

More often than not, however, owners consider each thoroughbred’s lineage when choosing a name, and some incorporate the name of either the horse’s sire (father) or dam (mother). But even in the absence of a family name, most racehorses find themselves saddled with something that at least seems significant enough to their owners.

For example, 2021 Derby contender Super Stock was partially named for his mother (Super Girlie) and because his owner felt he came from “good stock,” according to the Courier-Journal. Helium, meanwhile, was described as being “light on his feet,” his general manager told the outlet. And (arguably) the tastiest of this year’s horses, Soup and Sandwich, is owned by Charlotte Weber, whose grandfather founded Campbell’s Soup.

The origins of Degenerate Jon or Strip Tease, meanwhile, might be better left shrouded in mystery.