The Funnel and the Tube
The Magician looked out across the audience. "I'll need two volunteers- a man and a woman. Well, I see a lot of hands from among the men, but not so many- ah, you, lovely lady. Will you please step onto the stage? And you too, sir."
A slim redhead in a silver dress stepped up, her curly hair spilling to the middle of her back. A muscular man in a suit stepped up beside her. "Your names, please?"
"Bob."
"Samantha- Sammy."
"Now, Bob, please examine these objects." The volunteer looked at the items. A funnel starting at about 16" wide, but narrowing to about 4" at the small end, and a glass tube that was thick-walled, seven feet long (more or less) and about two inches wide.
While he was busy, the Magician pulled out some strong silk rope. "Now, Sammy. Would you mind if I tied you up?" Samantha gave the Magician a quizzical and slightly apprehensive look, then shrugged, and offered her arms. "There," the magician looped the rope around her wrists and pulled it taut. "Can't have you running away on us now. Especially once you see what's next.