Rolf Harris groped a teenage girl after she saw him crouched on all fours barking at a dog, a jury has heard.
The woman, giving evidence from behind a screen at London's Southwark Crown Court, said she was working as a waitress at a celebrity event in Cambridge when she was 13 or 14, and went outside when she and her colleagues heard the animal noises.
"He was on all fours and there was a terrier-type dog in front of him and they were barking at each other," the woman said.
"There was a small semi-circle of people around him laughing and Rolf Harris was playing up to the crowd."
Artist and television personality Rolf Harris arrives at Southwark Crown Court
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She said she felt "awestruck" at seeing the celebrity, whom she recognised "instantly" when she saw him outside the It's a Celebrity Knockout event in 1975 or 1976.
The woman, who is now 52, told the jury of six men and six women that Harris put his arm around her and moved his hand up and down her back, before squeezing her bottom.
With her voice wavering, she said: "I just stood there. I couldn't believe what was going on, this famous person putting his arm around me.
"To start, it was a very nervous but a good feeling. However, his hand then moved and his hand went up and down my back and his hand went over my bottom and it was very firm."
She told the court she had her back to the white marquee where the event was taking place, so the crowd could not see what was happening.
Rolf Harris denies 12 counts of indecent assault
The woman said: "I was too young to really understand the term but it was basically like groping. It was very firm and he squeezed it a few times.
"I was just completely frozen. I knew it was wrong. I couldn't move."
She said she was "extremely embarrassed" and moved away as soon as Harris let go of her.
"I don't know why I was embarrassed. I think when you are a child and you have someone doing that to you, it feels very awkward and you don't know how to react."
The woman is named in the second of 12 indecent assault charges that Harris, 84, from Bray in Berkshire, is facing, all of which he denies.
She said she could not remember detailed information about the day of the claimed grope because "the incident is bright red in my mind and everything else is grey".
The alleged victim told the court that she has "a physical reaction" whenever she sees Harris on television or in a photograph.
She told the jury: "It was Rolf Harris without a doubt and I can't bear seeing any image of him."
Earlier the jury heard from another alleged victim who broke down in tears as she claimed the entertainer assaulted her "out of nowhere" in a packed community centre.
The woman told the court Harris molested her when she went to get his autograph at the popular site near Portsmouth at one point between 1968 and 1970.
She told the jury that when she got to the front of the queue, Harris crouched down, signed her piece of paper and then touched her bottom and private parts.
"He was looking at me, smiling, and I was smiling, looking excited, and suddenly out of nowhere I felt his hand go down the back and up between my legs," the woman told the court.
She said she thought the first time might have been an accident, but claimed he did it a second time "aggressively".
"I thought 'what's going on?', because there were a lot of people around and I didn't process what had happened.
"He seemed such a nice man, I thought probably it was just an accident."
But then Harris allegedly touched her again, "aggressively and forcefully".
"It didn't matter if it was going to hurt me or not. It felt very aggressive and I knew that it wasn't an accident," she said.
The woman, who is now 52, said she felt she had moved out of her body after the alleged abuse.
"I think I went into some sort of moment where you are just out of your body and you're just thinking 'whoa I need to get away'," she said.
Breaking down, the woman told the court she "wasn't the same child" afterwards.
When asked how long she had memories of it, she said: "Forever. I can hear a song or something from that era and go straight back. I can shut my eyes and go straight back."
Harris, in a light grey checked jacket, with light grey trousers, a white shirt and yellow tie, listened impassively from the glass-walled dock as the woman gave evidence.
His wife Alwen did not attend court today, but other family members watched from the public gallery.
The woman said she remembered the alleged incident taking place around the time of the moon landing, and that Harris performed Two Little Boys at the event.
She said she could not call out about what had happened.
"I understood that it was wrong. I wanted to scream out 'What are you doing?', but it didn't come out.
"I didn't know how to put it into words. He scared me because he was looking at me all the time. His eyes were fixed and I kind of backed away, and I sat on a chair trying to process what was going on and looking at him carrying on as if nothing had happened."
The court heard that the woman told her family, husband, friends and a counsellor about the claimed abuse.
She said when she told her husband, "I said Rolf Harris was a dirty old man because he had put his hand on my bottom and between my legs when I was a little girl".
Defending, Sonia Woodley QC put it to the woman that Harris had never been to the community centre in question, but she denied this, as did two other witnesses who claimed they had been to the venue to see the performer.
The trial was adjourned until Monday.