An apparently standard 'phone call of the "my mouse isn't working" variety turns into:
"Does the cursor move at all when you move the mouse?"
"A little bit."
"Hold the mouse up above the desk and put your hand underneath. When you move the mouse can you feel the ball rolling along your hand?"
"There isn't a ball..."
"Ah. I think I know what the answer is..."
"...we lost that the other day so I put a Malteser in the hole."