Ms. Basil winnowed out the good dancers — “who could twist, who could jerk, who could pony?” Her first rule: no sneakers. “I auditioned some heavy hip-hop people — they couldn’t handle it,” she said. “The ’60s was leather soles and a wooden floor. That’s why the twist, the simplest dance, was such a sensation. Everyone could do it. They just swivel their feet and the upper body fell naturally in the opposite direction.”

Fifteen people were selected to be Playboy bunnies, circulating at the party. But after five hours of filming, Ms. Basil said, Mr. Tarantino had an idea: What if they danced?

Ms. Basil was tasked on the spot with creating a dance for four of the extras. Mr. Tarantino put them on apple boxes so they could be seen, but they were still behind a throng of dancing partygoers. “I knew it couldn’t be the pony, it couldn’t be the twist,” Ms. Basil said. “It had to be the jerk — the dance that is from the waist up.”

She worked quickly, constructing a movement chain from the go-go playbook. “These are nondancers,” she said. “They’re nervous. They’re learning unison in a bunny costume, in high heels, on boxes. Cameras are waiting. You instruct your strongest girl: ‘You call out the steps under your breath — like a ventriloquist, ‘Do the jerk, change, lasso arms, change.’”

Before the ’60s, Ms. Basil said, social dance “was partnering; it was the jitterbug.” But in the ’60s, partners split apart: “Freedom — what the ’60s were about.” Now, with dancers no longer holding hands, “arms started to dance,” she said, and the jerk, the swim, and the hitchhike appeared, each a dance for gesticulating arms.