When Sharon Tate arrived in Rome for filming near the end of March 1969, she was about three months pregnant and beginning to show. Because the script called for several semi-nude scenes, the director arranged to film those scenes first. As filming (and her pregnancy) progressed, the director obscured Tate's stomach with large purses and scarves. This is most apparent in the scene following her ride in the furniture mover's van.
Terry-Thomas remembered Sharon in his 1990 autobiography "Terry Thomas Tells Tales": "On the first day of filming 12 Plus 1 on location in London's Jermyn Street, Sharon Tate came up and introduced herself. She said, quietly, 'I must tell you something before we start working together. I can't act, but I somehow get by without anyone realizing, so don't worry.' Actually, Sharon turned out to share a distinction with Lena Horne - they were the only two performers I ever knew who were entirely 'natural' before the camera. Everybody else, method actors (and T-T too!) automatically took on a different stance and manner, as soon as the cameras started rolling. So there were no difficulties with Sharon. We were like a double act. She was nice, intelligent and pretty. I wish I had been able to see the finished film. I've never been able to catch it."
Loosely based on a famous 1928 Russian novel by Yevgeni Petrov and Ilya Ilf, which was also filmed only a year later as The Twelve Chairs (1970), directed by Mel Brooks.
Terry-Thomas explains the plot of a book he is reading to Sharon Tate called "My Name Is Lust". The copy of the book he gives her has the title pasted over the cover of an existing paperback novel, the 1969 Corgi Books printing of "The Thing Of It Is" by William Goldman.