"Prove something other than your own mind?"
"Oboy! is it time for my famous Desk Test?" The Cartoon Dog pulled at the desk by the wall, dragging it out to the center of the room.
"Nope, they're not going to fall for that anymore." The Stoic Cat, standing square-shouldered, held his paw out against the desk, blocking its continued movement across the floor. "Not since we've proven that the desk itself is a figment of your imagination, and the pain in your hand is merely an extension of that imaginary context."
The Cartoon Dog dropped its paws and stared stupidly into space. "Aw, gee. That kinda takes the fun outta life." He stumbled towards the door. "Wait, I have an idea!" The Cartoon Dog raced over to the Stoic Cat, grabbing its arm.
"Hey, what are you doing?"
The Cartoon Dog hesitated for a moment, and then answered. "Look, if I smack my hand on the desk, then you would say that the desk is a figment of my imagination and not yours, and that the pain in my hand is real only to me because the desk is only real to me, and my interaction with this desk is only real to me, which is why only I feel the pain of having smacked the desk with my hand."
The Stoic Cat shrugged, "Yes, so?"
The Cartoon Dog grinned, "Well, if I smack your hand on the desk, and if you feel the pain in your hand, then it will prove that this desk is not a figment of my imagination, since your interaction with this desk results in you having the pain. I cannot imagine you having any pain."
The Stoic Cat exhaled dismissively and stared upward in exasperation. "You have a dizzying intellect. Go ahead," he continued. "Dazzle me with your brilliance! Baffle me with your--your--oh, whatever you call that stuff in your skull!"
The Cartoon Dog held the Stoic Cat's paw high over its head and began to explain. "Now, if my smacking your hand on this desk causes you intense pain, please let me know immediately." He hoisted the Cat's paw up a little, preparing to bring it downward rapidly.
The Stoic Cat suddenly looked downward. "Hey, wait. This would still prove nothing, wouldn't it?"
The Cartoon Dog paused. "What? Whaddaya mean, prove nothing?"
"Well," The Stoic Cat explained, "If this desk were a figment of my imagination and not of your imagination, then it is quite likely that you are a figment of my imagination as well, and therefore, your claim of having experienced pain was only my imagination pretending to portray realism."
The Cartoon Dog scratched its chin thoughtfully. "Hmmm, I never thought of that." He glanced around nervously, pondering the conundrum that had just transfixed his mind.
The Stoic Cat concluded, "And you are a Cartoon anyway."
The Cartoon Dog grimaced and snarled quietly, "You keep saying that like it should offend me. I know how to answer this! He grabbed the Cat's paw, reached it up high over his head, and shouted, "I'll smack your paw on this desk, and then I'll strike you dead. If the desk is still here, then it cannot be a figment of your imagination."
He brought the Cat's paw down on the desk rapidly.