Once on a research cruise in the Pacific north east, we had some folks from the Office of Naval Research (US Navy - ONR) using air drop sonobouys as potential listening devices for submarine earth quakes (we just basically busted the sonobouys out of their deployment tubes and I'd pitch them over the side for them as they signaled, then the bouys deployed normally).
Every night for several weeks we did this (the submersible, ALVIN was down during the day, so these quake ops were done at night). But, there was nothing coming up on the sonobouy traces.
So, I was tasked with making something happen. I took a net bag and filled it with some light bulbs, empty ketchup bottles and other odd empty but sealed glass containers, then weighted it with some scrap chain, and surreptisiouly dropped the whole thing over the side.
The ONR officer ran all over the ship telling everyone of the data "hit" of a small swarm of micro-earthquakes (the bursting glass apparently did make a trace just like a bunch of small micro-quakes would). Of course, the last person she came to was me (I was in the lab, extracting DNA from tube worms), and I made some comment about my, how fortunate it was they finally had some real data, on the last night with the last batch of sonobouys and all. WoW, what a unbelievable break. She went real quiet for a minute as she processed this, and then started cussing me out like, well, a navy person.
In terms of execution and effect, that was one of the best practical jokes we ever pulled on a cruise.