It is one of the most lurid and complicated legal cases in recent Canadian history.

A group of lawyers are contending that a man did nothing illegal when he had the family dog perform oral sex on his step daughter. Government attorneys are adamant that the man needs to be found guilty, if the law is expected to protect children from bestiality. And animal rights activists are arguing that the man's actions are not just morally outrageous, but animal abuse.

All three sides entered the top courtroom in Canada on Monday to lay out their respective cases before the perplexed justices of the Supreme Court.

The core question of the case is this: did Parliament, in writing a law criminalizing bestiality, intend to forbid oral sex, or just penetrative sex?

Arguing before the court on Monday morning, no lawyer was able to give a concrete answer.

This is seemingly the first case in Canadian history that has raised the question, leaving very little in the way of case law to help the judges find an answer.

The legal quandary began when a man — whose identity is protected by a publication ban — was tried on 14 criminal charges. The majority of those charges involve sexual indecency and child pornography, but he also faced two charges of bestiality: one, for bestiality itself, and another for counseling his underage step-daughter to commit bestiality. At trial, the judge found the man guilty of many of the charges and sentenced him to 16 years in prison.

The man was ultimately acquitted for the second charge of counseling his step-daughter, who was 15 or 16 at the time, to commit bestiality. But, because he was the one to bring the family dog into the bedroom and have it perform oral sex on his unwilling daughter, and because he videotaped it, he was found guilty of the other bestiality charge.

That one conviction, however, was appealed.

His lawyers contended that because bestiality was always tied to "buggery" — a centuries-old English crime that specifically meant anal intercourse, usually between men — proof of penetration was required in order to convict someone of bestiality.

The Canadian Parliament passed laws in 1955 that specifically criminalized "buggery or bestiality." In 1985, the law was updated to create a new law that forbid bestiality on its own, especially with children. At no point, however, was bestiality defined.

The man at the center of the case convinced British Columbia's Court of Appeal, with two-of-the-three judges ruling that, historically, bestiality was only ever meant to include penetration.

The battle wasn't over, though, and the case was sent up to the Supreme Court.

One question that remains is about financing the legal challenge. Litigating a case through every level of the court is no cheap affair and it's unclear whether the legal team (compromised of two lawyers in Vancouver and one in Ottawa) trying to preserve the narrow definition of "bestiality" is being paid, or whether those lawyers have taken on the case pro-bono. When Eric Purtzki, a member of the man's BC legal team, was asked whether he was doing the case pro bono and, if not, where the money was coming from, he refused to answer.

Also joining the case before the top court was Animal Justice, a registered charity that takes on animal rights cases. Their intervention marks the first time that an animal rights group has argued before the Supreme Court.

The morning began with lawyers for the Attorney General contending that the law's intention was always to criminalize any sort of sex with animals.

"Bestiality is bestiality," said Mark Levitz, a lawyer for the government of British Columbia. "Such acts offend our basic moral values."

But the judges weren't sold.

"I don't think any of those are good things," said Justice Russell Brown, referring to non-penetrative sexual acts with animals. "But I think you're reading into a section of the [law] that doesn't say any of those things at all."

Justice Rosalie Abella, generally considered one of the more left-leaning judges on the top bench, asked whether the law had any consideration of the well-being of animals. Levitz said it did not and that, instead, it was more concerned with protecting children and maintaining a moral standard.

The lawyers for the man convicted of sexually abusing his two teenage daughters had an equally difficult task.

"There's no absurdity in retaining bestiality as requiring penetration," Purtzki argued. "It may not go far enough but it still does protect children."

He argued that, if Parliament wanted to criminalize oral sex with animals, then it would have added a definition, or it would have used a new word, instead of carrying over the antiquated language.

The justices weren't quite buying that, either.

Abella asked specifically whether forcing an animal to perform oral sex on a child is criminal. Purtzki admitted it was not.

"Does that make sense?" Abella asked.

Justice Michael Moldaver followed a similar thread. "Are we to take it that society in those days didn't take it as unnatural for a human being to have oral sex with an animal?" he asked.

Animal Justice, on the other hand, argued that the courts need to look at bestiality from an animal welfare perspective, in addition to any harm it may have on children, or the moral fabric of society.

"I'm not asking you to give animals the vote," Peter Sankoff, a law professor at the University of Alberta who was arguing for the group, told the court.

"There's different forms of harm [animals] could endure as a result of this type of conduct," he added. "This is 2015 and our moral values change, and the content of the charge needs to be adjusted accordingly."

Camille Labchuk, who is also counsel for Animal Justice, told VICE News that the Supreme Court has the option of pronouncing itself on animal rights in a way that it has never really done before. The fact that Animal Justice was allowed to intervene in the case certainly raises that possibility.

"They're taking it pretty seriously," she said.

Follow Justin Ling on Twitter: @justin_ling