Looks like catsup squirting out of the bottle. Very startling.

This is a sight gag and looks just like you're squirting catsup or mustard on the victim. The secret to pulling off this prank is timing. Most people execute this prank way too fast. You have to take your time and make sure the victim gets a good look at the catsup or mustard bottle. You'll be surprised -- they won't even notice the knotted string at the end even though it may seem completely obvious to you. That's because they're not expecting it. Approach the victim with the mustard or catsup so that they get a good look at it. Then ask if they need some mustard and give it a good squeeze. The string comes flying out and looks like you're squirting mustard or catsup all over the victim. When done properly, this always gets a reaction. The victim will invariably jump back and look at their clothes for evidence of the mustard or catsup. Feed the string back into the bottle and you're ready for the next victim.

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