This reminds me of a highschool prank I pulled on a friend. I realize it won't work for you, but thought I might share the story.
Background info but funny: One day we were sitting in another friend's living room, and he saw muffin shaped things near the fireplace. He said, "Oh muffins!", grabbed one, and took a bite. Well they were wax-like firestarters and even had a clearly visible pinecone sticking out of the middle. So we all laughed.
Prank 1: The next week, we thought we could continue the joke and make muffins. One muffin we tainted (tons of tobasco sauce and a tablespoon of salt were poored into the middle of the muffin before baking. We all had muffins, and gave him the tainted muffin. The first bite was innocent, and he liked it. The second bite however hit the center and he spit it all out gagging.
Prank 2: We were prepared. We had a can of Mt. Dew that we opened the slightest crack (you can do this and leave no visible trace with the can tab, no need for complicated drills or needles). Turn it upside down for ~2 hours for everything to drain out of the can. Emerse in a bath of vinegar (about the same color as Mt. Dew). 2 hours later it is full of vinegar. Wipe down the can to remove the traces of vinegar. Place in fridge to cool. Grab all of the glasses in the house, sprinkle a bit of baking soda in the bottom of the glasses.
Friend spits out the muffin, begging for something to drink. Open a cupboard, grab a prepared glass, open the fridge and grab the prepared Mt. Dew. Open it up (since the tab was never fully opened, the sound is still there, and since he is gagging he doesn't realize the sound is slightly different from lack of pressure). Poor into glass. Vinegar + baking soda = bubbles. He sees the yellowish liquid with bubbles. He says thanks, takes a big swig, and spits that out.
It was so funny.