Door to Silence

New Orleans, Louisiana. While attending the funeral of his father, Melvin Devereux (John Savage), meets a beautiful young woman (Sandi Schultz) who addresses him by name, although he cannot remember having met her before. After an enigmatic exchange of casual words, Devereux drives away, motoring aimlessly around New Orleans. Devereux decides to ignore warning barriers and drives onto a closed freeway. But the police follow him and he is forced to turn aside. His car breaks down in a delapidated area of the city. But the mysterious young woman again appears, driving a red sports car. The mystery woman suggests that he try a mechanic located nearby to fix his car. After helping Devereux push his car to the garage, the young woman again refuses to explain how she knows him or tell him her name. While waiting, the woman suggests they go to a motel nearby, apparently for sex. After checking into a room, and getting ready in the bathroom, Devereux exits and discovers that she is gone, leaving behind a message written on a mirror in red lipstick which says that the time is not yet right.
Having collected his repaired vehicle, Devereux encounters a hearse driving on the road ahead. When he attempts to overtake it, the driver (Richard Castleman) deliberately swerves to prevent him. Turning off onto more treacherous country roads, Devereux nearly gets stranded when his car gets stuck in muddy terrain, and he barely negotiates a rickety wooden bridge.
At last finding his way back to the main road, he stops off at a local roadside bar for a drink where the hearse is also parked outside. In a drunken altercation, Deveveux challenges the driver to reveal whose body he is transporting. The folded ribbon adorning the casket seen inside the hearse bears a name tantalizingly similar to Devereux's own. The confused, now frightened man follows the hearse to a church where an all-black congregation is mourning at another funeral procession. Devereux drunkenly disrupts the proceedings, attempting to look inside the closed casket. He gets thrown out of the church by the angry parishioners.
Devereux drives over to a nearby funeral home where he sees that all of the corpses in the open coffins are labeled 'Melvin Devereux'. He finds his doppelganger lying dead in one of the caskets and tries to touch it, but it disappears beneath his outreached hand.
Back on the road, Devereux picks up a beautiful female hitchhiker, and tries to respond to her seductive advances, but he cannot perform, forcing her to leave the car. Next, Devereux drives onto a river barge as it transports a handful of vehicles, including the omnipresent hearse, to the other side of the river. Devereux rips open the hearse's back door and tries to open the coffin which clearly bears his name. The hearse driver intervenes and there is a struggle. Devereux is subdued by the other barge passengers and gets arrested. In a local courtroom, Devereux is given a fine for defiling the casket. Devereux drives away and soon stops to visit a tarot reader. Reading the palm of his right hand, the palmist tells him that he has been dead for several hours. She suddenly falls dead after receiving a phone call from a "Mr. Devereux."
Devereux is once more on the road, driving nowhere. He suddenly sees the hearse again on the road and tries to overtake it, only to crash head-on into an oncoming truck. Devereux is killed instantly. His wristwatch stops at 7:29 PM, the same time as the film's prologue where a briefly seen car crash had appeared to be the cause of his father's death. The mysterious woman observes the fatal accident a short distance away on the road before getting into her car and driving off. The number license place on the woman's car reads: D.E.A.T.H.

Question: Devereux challenges the driver of the hearse to reveal what?
Answer: Whose body he is transporting