What you need:

- A standard pen
- Some tape
- A stick of dry spaghetti
- Some kind of sharp object (screwdriver possibly)

We used to make these as kids at school. :)

NOTE: Sorry some people seem to have gotten the wrong idea. I should of been more clear of

HOW IT WORKS:
Inside the pen is still the ink tube, the spring, and a little white cap the ink tube fits into.

when you push the ink stick in, it get stuck inside the cap. as you pull it back, it creates tension in the spring. When pull back the ink stick far enough the white cap pops off the ink stick and flies forward from the tension of the spring.

This strikes and shoots a small piece of spaghetti quite far.

Step 1: Break Pen in Half

Snap the pen where the coloured and transparent parts meet.

Step 2: Dig Out Button

Use a screw driver or sharp object to scrape away at the plastic at the top of the pen to remove the button.

Step 3: Enlarge Hole

Enlarge the side hole using a sharp object so that its just large enough for the very tip of the transparent bit to fit in.

Step 4: Start Construction

Place the transparent bit small side down into the hole, and tape in position.

Step 5: Finished

Continue taping making sure the "spaghetti feeder" is still in the hole.
Place in some spaghetti when you are done.

NOTE: What I've done here is a little bit wrong. I've notice that when the feeder is at an angle like this sometimes the spaghetti jumps out of the top. Its best to keep it straight if you can.

Step 6: Shoot Things!

Do this by pushing forward, then pulling back the ink tube.
You can do this over and over again and watch the spaghetti slowly go down into the gun as it gets shot out the front.

Fires quite far too.

Step 7: How It Works.

Quick pic.
Just to show you how it works and how extremely simple it is to use.
You can push the ink stick forward and pull it backward very rapidly firing a lot of spaghetti.