Card Trick

Card Trick: The Internet Lie Detector

Welcome Magicians! This page reveals how to operate the Internet Lie Detector, an extremely effective card trick designed by Jim Bumgardner, the programmer behind these other computer-aided card and mentalism effects:

The effectiveness of this trick depends on its method of operation remaining a well kept secret. Therefore, don't reveal the secret of this trick to your intended victim. Thank you very much!

The Effect

You bring an unsuspecting co-worker into your office or cubicle and say "Check out this website! This company actually figured out how to make a LIE DECTECTOR using HTML! It's awesome!" etc. etc.

You then proceed to the following address:

Note: this site won't be functional until you read the rest of this document.

When you get to the website, you follow the instructions on the first screen which tell you to select a random card. You ask your co-worker to name a favorite playing card. She writes the name of this card on a post-it and sticks it to the monitor while you proceed to the next page.

The next page tells you that you will be asked a series of questions about the card. You are free to tell the truth or lie. You both read the instructions on this page, and then continue on to the next page.

The next page contains the first question: "Is the card a joker?"

You ask your co-worker which answer she wants to use, "yes" or "no". As instructed, she may tell the truth or lie at her own discretion. You prepare to click the appropriate button and then say "Hmm - actually YOU should be doing this..." (meaning your co-worker). You then vacate your chair, and put your co-worker in the drivers seat. From here on out, you don't touch the computer.

Your co-worker now responds to the computer's questions. Each time, the computer does indeed determine correctly if the co-worker is lying! It will eventually use the answers to narrow down to the correct card - this may take anywhere from 4 to 6 questions, depending on the card (face cards are faster).

Later, when your co-worker visits the same website, and attempts to use the service, she will get a message which says "Sorry! The Internet Lie Detector is currently down for upgrades. Come back later!"

How it Works

The Internet Lie Detector is a handful of HTML and Perl scripts written by Jim Bumgardner. Needless to say, the program is not a lie detector. Rather, it already knows the card once the yes/no questions start, because the magician communicates this information to it during the first two mouse clicks (which were used to wade thru the instruction screens).

If you'd like access to the source code, or would like a customized version for your own use (or have other computer consulting needs), you can contact Jim via his website:

How to Operate

To use the Internet Lie Detector, you must first unlock it.

You start by visiting the following URL:

Note: A previous "retro" version (called "i polygraph") is also available at

This screen is mostly blank with a single "Continue" button.

To unlock the trick, you need to click just *outside* the button, and NOT *inside* the button. If you click inside the button, the trick will "lock" and it won't work properly. This is to prevent your friends from figuring it out.

When the trick is unlocked, you will then get a screen asking you to select a card and write it down on a piece of paper (if you have a deck, you may force a card on the spectator, if you like).

This opening screen also has a "Continue" button at the bottom:

When you press this button, the script pays attention to where inside the button you press, because the button is mapped.

HELPFUL HINT: If you use Internet Explorer instead of Netscape, you won't get the give-away "coordinates" feedback when you pass the mouse over the button.

Each button is divided into 8 sections, like so:


So, for example, if the card were a Queen of Diamonds you would click here, inside the button:


The next screen (which says "Now please rest comfortably") also has a "Continue" button which you must click on to communicate the remainder of the information.

You use the following grid layout if the card is a low card:


And you use the following grid layout if the card is a high card:


Note that jokers are considered high cards.

You will now be asked the first question. From here on out, you may give the mouse to the spectator, because the trick is self-running from this point.

Once the trick is over, wrestle control back from your co-worker by feigning an interest in actually getting some work done. Reveal nothing and don't do the trick again! Be kind: suggest that he or she go show it to someone else! Heh heh heh...

If you *MUST* do the trick again (and you really shouldn't), the last screen has a "Continue" button on it which may be used to lock and unlock the trick in the same manner as the first button.

Happy Conjuring!

-- Jim Bumgardner