Live, packaged, MS 10 under the top table with a suitable length of cord.
Small piglet released at an apt moment.
A nice pat of CPX in the grand piano with a cunningly set timer.
Model helicopter display.
Battleships (if you know, you know!).
Silver nitrate crystals on a wooden floor.
Iron filings buried in the candles.
A Wimshurst generator (hidden) connected by micro copper wire to cutlery and silver.
A spare camel (Aaaah Masirah days)
We once borrowed a dumper truck - brought in to T****y I****d mess
And many, many more - most subject to sanction by health and safety, COSH,Road Traffic Act and various international treaties and supervisory bodies.
Be prepared to perform OO/SDO for a while afterwards.
good luck,
Lurkio.