Aah, it's *that one*. Our chemistry teacher made us memorise the periodic table up to and including the line before (final memorised line starting with Potassium). The mnemonic supplied involved simply stringing the symbols together and speaking them as one long nonsense-word. I can remember it to this day :)

And, I have seen such a video. It involved a large glass dish of water which was in several pieces by the end of the demonstration.

Our chemistry teacher promised us that if the school were ever to want rid of the (old falling-down Victorian) swimming pool, she would buy some caesium and let us all watch her drop it in the water. Strangely they never did.

Sounds like the thing one of our chemmie teachers was notorious for, though he had a silly tune to go with it.