The legend was also asked about hooking up with Tom Cruise, while Corden was grilled about his least favorite Carpool Karaoke guest.
The singer appeared on the show to promote "Mama Mia 2," but left taking a bite of out a few nasty delicacies in another disgusting game of "Spill Your Guys or Fill Your Guts."
The rules of the "Truth or Dare"-themed game are simple: Each contestant gets to choose between answering an incredibly revealing question about themselves or their work, or swallow some gross items like dried caterpillar, cow tongue, scorpion, fish & chips and musty peas smoothie, haggis -- which Corden lovingly described as "savory pudding that contains sheep's heart, liver and lungs all encased beautifully in a sheep's stomach) -- or a 1,000-year-old egg.
Corden was up first, as Cher asked him to reveal who was the "drunkest person" at the royal wedding or eat that damned egg. While James admitted he knew "exactly who it is," he didn't want to get in trouble with them and took a bite.
Next, the host said to his guest, "You've said Tom Cruise is one of your Top 5 favorite lovers. Who are the other four?" She didn't even hesitate before throwing back some dried caterpillars, adding that she didn't even remember saying that. "But do you remember doing it?" he asked. "Yep!" she answered immediately. He wondered if Cruise "went straight into the Top 5" when it happened, with Cher adding, "No, I had to give ratings."
It was Corden's turn to squirm again as she then asked, out of Britney Spears, Miley Cyrus and Mariah Carey, which of them would he "least like to sing with again" after doing "Carpool Karaoke" with all of them. Cher even said she knew "who it is." While the audience screamed for him to spill some tea, he refused, said "I can't" and took a gulp of that sickening smoothie.
The game ended with Cher promising to answer whatever Corden threw at her for his final question, but she ended up eating her words -- and cow tongue -- when he asked, "You have been, rightly so, very outspoken about your disapproval of Donald Trump. Say one nice thing about him."
See her chow down like a champ above -- and watch more "Spill Your Guts or Full Your Guts" videos below!