Lubors Lens by Paul Harris
Your friend holds a pen on her open palm as you hold a clear Credit Card Protector just above the pen.
You show a bizarre optical illuzion...and give the plastic lens a twist. The center of the pen suddenly becomes TRANSPARENT...and then completely INVISIBLE! She can even see right through her spread fingers where the center of the pen was a moment ago! Another twist of the lens and the missing pen center suddenly becomes VISIBLE AGAIN!
BUT THAT'S JSUT THE WARM UP! You then slowly twist the lens again...and in full view the center of the pen visibly DISTORTS...then MELTS into a WEIRD TWISTED MESS!! But this time the optical illusion is REAL...and the weird twisted shape is now a PERMANENT part of the pen...You can even let your friend keep the deformed pen as a souvenir. And yes, it still writes!
THERE'S NO EXPLANATION!...except that the lens is not a thing you'd want near any of your favorite body parts.