The Spy Who Came in From the Cool - S1-E5
Continuity mistake: In the karate dance number there is a girl in a red outfit behind Mike on the floor. She must change her position at least four times in ten seconds - she can be seen moving and laughing with the girl beside her on the floor.
Answer: The Monkees TV series was very much a fantasy (this was the "groovy" psychedelic 60s, after all). Impossible things, such as items appearing out of nowhere, happened on their show without explanation all the time.
Jean G