Continuity mistake: When Davy is telling Mike and Peter that Otto and Sigmund are trying to kill Bettina, the sandwich Mike has switches from his left hand to his right hand in a split second.
Continuity mistake: When David is telling Michael and Peter about the plot to kill Bettina, Peter's hair swaps between a middle parting (in the wide shots of David, Michael and him) and a side parting (in the closeup of just him and Michael).
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