Serial killer Joanna Dennehy was driven by a thirst for blood as she sought out further victims, a court has heard.
Mark Lloyd was in the same car as Dennehy and her alleged accomplice, Gary Stretch, as they searched Hereford before she attacked and repeatedly stabbed two people in the street.
The pair were already wanted by police following the murders of three men in Cambridgeshire and the 31-year-old serial killer had likened herself and Stretch to Bonnie and Clyde, Cambridge Crown Court was told.
Being cross-examined by Stretch's counsel, Karim Khalil QC today, Mr Lloyd said he had been scared of Dennehy and had no choice but to join the pair on the journey from King's Lynn, Norfolk, to Hereford.
He added: "If she had told me to put my head through the windscreen, I would have done."
Dennehy, of Orton Goldhay, Peterborough, has admitted murdering Lukasz Slaboszewski, 31, John Chapman, 56, and Kevin Lee, 48, who were found dumped in ditches in March and April last year.
She has also admitted the attempted murders of Robin Bereza and John Rogers and preventing the lawful and decent burial of all three murder victims.
Stretch and another man, Leslie Layton, are standing trial accused of helping her dispose of the bodies and covering up her crimes.
Jurors have been shown pictures of Dennehy smiling and posing with a knife shortly after murdering the men.
In another picture she flashes her bra and shows off self-harming scars.
Stretch is photographed mimicking her pose and making an obscene gesture to the camera.
Describing the moment he found out the pair were wanted by police, Mr Lloyd said: "I thought it was Gary who done the murders because he's 7ft 2in and looks like Herman off The Munsters.
"She looks like butter wouldn't melt until she opens her bloody mouth."
Mr Lloyd told the court that, as they made their way to Hereford, Dennehy had said: "I want to have my fun."
Dennehy had made it clear she wanted "a man with a dog" and Stretch had helped with this search, he added.
Describing the attack on the first man, Mr Bereza, he said: "I thought she was going to mug him but then it twigged on me.
"I thought 'You just want blood'."
After the second attack on dog walker Mr Rogers, Dennehy climbed back into the Vauxhall Astra driven by Stretch.
She was carrying Mr Rogers' whippet and told the pair: "It's me only friend."
Mr Lloyd went on: "Afterwards, Gary drove off very, very calmly. It was as if they'd just stopped for McDonald's."
Stretch, real name Gary Richards, 47, of Riseholme, Orton Goldhay, Peterborough, denies three charges of preventing the lawful burial of all three men and two counts of attempted murder.
Layton, 36, of Bifield, Orton Goldhay, denies perverting the course of justice and two counts of preventing the lawful burial of the bodies of Mr Chapman and Mr Lee.
A third man, Robert Moore, 55, of Belvoir Way, Peterborough, has admitted assisting an offender and is awaiting sentence.