Construct a inexpensive hydrophone out of things laying around your house.
I decided to put up this instructable because (to my surprise) no one has a hydrophone instructable up yet. I made mine using a mixture of other people's hydrophone creations that I found through a google search and a bit of ingenuity.
Here's the parts that I used but it should be fairly easy to adapt whatever similar items that you can find.
knife or scissors
( I used a small spray bottle that was originally some "energy-caffeine spray")
Step 1: Breaking Down Parts
You are going to dissasemble the computer mic so that you have the capsule and the cord seperated, I didnt put any pictures of this up because I already disassembled them before deciding to make an instructable, but the proccess is pretty easy and is a little different with every mic.
You also should have your bottle or container taken apart.