This is a avery simple April Fools Joke. It can be played on anyone but the more intensely focused a person is the better. I used it on my manager and several others and I got everyone. Some play acting is required.
2 BIC Pens (you know the 100 pack ones you can get at the drug store)
a victim or two or three or four
Step 1: Open the Pen
Take the cap off the pen and gently pull on the writing part of the pen it should come apart fairly easily.
At this point you have:
a pen filler
a pen cap
a hollow pen with one plug in an end of it