Pointless fans watched on as the BBC host spoke to contestant Linda, but ended up making a jibe about her looks.
The PA for a water utility company in the Midlands was first asked her opinion on the quiz board and to give a Pointless answer.
Alexander asked: “Linda, what would you like to go for? We’ve got some moderately extreme scores here.”
Linda replied: “Yeah, there’s one I definitely know that’s left and there’s one that I really want to go for, but I’m not sure I’ve go the nerve.”
The show host then tried to give a boost of confidence, saying: “I bet you know it. I bet it’s right.”
Hesitantly, Linda said: “I’m going to say. I’m going to regret this, but I’m going to say South African Formula 1 world champion – Jody Scheckter.”
Alexander repeated her answer, saying: “Jody Scheckter says Linda,” as the contestant confirmed with a “yeah”.
The 48-year-old presenter then said: “Do you know what? You looked like a ventriloquist when you said that.”
Confused, Linda pointed at her face and sighed: “Sorry. That’s the lines.”
Horrified that his words had sounded like an insult, Alexander rushed to explain himself, saying: “No it’s great. No, not like the dummy, you looked like the…”
Embarrassed, the audience chuckled, but luckily Linda laughed it off and jokingly snapped back: “Thanks very much!”
Alexander continued: “You said it… you said it without moving your mouth. It was extraordinary,” prompting Linda to smile: “I know.”
It comes after Richard Osman made a big revelation about the contestants that appear on the BBC One quiz show on yesterday’s show to his co-host Alexander.
The Pointless pair teased how contestants made up of family duos always cause chaos on the show, with Richard confessing they always “fall out very badly”.
Noting the line-up, Richard added the show comprised of groups of friends, saying: “The only returning pair from that show, Gavin an Nick, who are where they should be on podium one.
“It’s quite nice, isn’t it? They did well. They did do very well last time, yeah. They’re going to be tough to beat, I suspect.”
Alexander noted: “And friends, it’s a friends show! We’ve had a lot of parents and children.”
Richard then dropped his “fall out clanger”, adding: “That’s true, that’s nice isn’t it? No family.
“Because quite often when we have family shows they fall out very badly.”
Alexander gasped: “They can! Oh, they can.”