On “Killer Karaoke,” contestants sing karaoke while performing stunts. (Adam Rose/Turner Entertainment Networks)

A lady sings. She sings and walks. She walks through a tub of rotting fish guts, a tub of maggots, a tub of biting lizards. Yet she keeps singing. “You give me fever,” she sings. But wait, is she singing … or screaming?

When she comes to a tub with an alligator, she halts.

Bugs and bites are but a few of the obstacles contestants face as they try to keep on singing and win up to $10,000 on “Killer Karaoke,” a TruTV series that the New York Times called “the greatest show in television history.” It’s back for a second season (Thursdays, 10 p.m.) with rock and roller Mark McGrath replacing stunt comic Steve-O as host and a tweaked format in which the audience votes for its faves.

And really, the show is pretty great. It’s as if “American Idol” and halfpipe skiing had a baby that was raised by the Marquis de Sade: music + insane physical ordeals + sadism!

True, “Killer Karaoke” is sophomoric and cruel. But ultimately, it is about the indomitability of the human spirit, which will not let snakes, scorpions or stink beetles keep it from expressing itself in song.