Some Supreme Court justices had tough questions for a Florida lawyer about whether the state's lethal injection method causes excruciating pain for death row inmates.

Justices were taking up the latest capital punishment debate that focuses on the trio of drugs used in Florida and most other states.

"Your procedure would be prohibited if applied to dogs and cats," Justice John Paul Stevens told Florida Assistant Deputy Attorney General Carolyn Snurkowski.

Justice Stephen Breyer said that a medical journal study found that inmates can suffer pain under the three-drug combination and it "doesn't seem too difficult" to alter the medicines.

Snurkowski said that it would be up to the inmate to detail a new method, an argument that seemed to anger several court members.

"Doesn't the state have a minimal obligation on its own" to investigate whether its executions cause gratuitous pain, Justice Anthony M. Kennedy asked.

The high court is delving into a limited part of the subject: whether inmates can file special last-minute challenges to the chemicals used in lethal injection even if they've exhausted all their regular appeals.

Even still, the justices had a wide-ranging discussion about the way executions are carried out, and how they can be contested.

Justice Antonin Scalia said that if justices allow Florida death row inmate Clarence Hill to pursue claims, that could drag out a case that has already been pending for more than two decades.

Hill, convicted of killing a police officer, was strapped to a gurney with lines running into his arms to deliver the drugs when the Supreme Court in January intervened and blocked the execution.

He claims that the chemicals used in Florida executions and by many other states — sodium pentothal, pancuronium bromide and potassium chloride — can cause excruciating pain. The first drug is a pain killer. The second one paralyzes the inmate and the third causes a fatal heart attack.

Justices have never ruled on the constitutionality of lethal injection, which is used by the federal government and every state that has capital punishment except Nebraska.

In this case, they can give inmates new authority to challenge lethal injection as unconstitutionally cruel. The court's decision to hear the case renewed legal efforts around the country on behalf of death row inmates, and executions have been stopped in California, Maryland and Missouri.

If the court allows Hill to file a civil rights action, "it will be a stamp of approval from the United States Supreme Court for these challenges to go ahead," said Deborah Denno, a Fordham Law School professor.

She said the outcome may not reveal much about the new court.

Chief Justice John Roberts replaced the late William H. Rehnquist, and Justice Samuel Alito replaced the retired Sandra Day O'Connor.

O'Connor wrote the court's 2004 ruling in its last lethal injection case. Justices said that Alabama death row inmate David Larry Nelson could pursue a last-ditch claim that his death by lethal injection would be unconstitutionally cruel because of his damaged veins. He argued that prison staff would have to cut into his flesh to get to a vein.

Kent Scheidegger, legal director of the pro-death penalty Criminal Justice Legal Foundation, said, "Hill's failure to follow the rules governing that process should not be rewarded by the opportunity to delay his well-deserved execution with a last-minute challenge in the form of a civil rights lawsuit."

Hill was convicted of killing Pensacola Police Officer Stephen Taylor in 1982. Taylor's family is growing weary after 24 years of delays and want Hill, now 48, to be executed.

"It needs to be done and it needs to be over with," said Linda Knouse, the slain officer's sister.

The case is Hill v. McDonough, 05-8794.