As far as Halloween pranks go, soaping up windows, throwing toilet paper in trees, smashing pumpkins—it’s all passé. This is the second decade of the 21st century. It’s time to use modern science to really make Halloween horrifying.

Here are five ways to use a little DIY chemistry to really freak out the neighbourhood. Actually, this stuff might not come off as genuinely scary—in fact, if you’re a responsible adult, it’s all totally harmless. But each experiment is indeed either loud, bright, shocking, or extremely stinky. And if you can successfully pull off these five projects, any trick-or-treater will think twice about ever lighting a bag of poo on your doorstep again.

Sure, burning hair makes a great stink bomb, but who wants to deal with collecting other people’s hair? Yuck.

You can make a more hygienic, flame-free stink bomb from matches and ammonia. Just slice the sulfur-based heads off 20 matches, and put them in an empty plastic bottle. Add two tablespoons of household ammonia (actually, the ammonia is pretty horrible smelling all by itself). Shake it up, wait a few days, and you’ve got some god-awful smelling stink bomb juice.

What you do with it next is up to you—but a disposable squirt gun can make an effective delivery mechanism. And it’s so much less wasteful than tossing eggs. Just wear impermeable gloves, for the sake of stinky fingers, and, you know, prints on the weapon.

You’ll need to invite your victims over for some bratwursts on the grill, but the effort will be worth it. Just take a mostly empty ketchup bottle, and pour in one and a half teaspoons of baking soda. (Do not shake—you’ll start the chemical reaction prematurely.) Close the lid tightly.

Now, grill the brats. Set out the condiments. The unsuspecting ketchup user has to shake the bottle—that “ketchup” has gotten all settled in the bottom. Then, when the lid opens…BAM! There’ll be so much red ooze everywhere, it’ll look like an outtake from the Texas Chainsaw Massacre right there in your backyard.

It’s polite to have a backup bottle of regular ketchup ready in case anyone still wants to stick around and eat.

Methylene blue is often sold at pet stores, as it is a treatment for tropical fish diseases. Now, the interesting thing about methylene blue is that, if ingested, it can temporarily change a person’s urine colour. The effects range from a faint green tint to a bright blue stream.

For the vast majority of people, a tiny dose of methylene blue is harmless. So slip a tablespoon into a 2-litre bottle of cola and serve it at your bloody barbecue. That should give the guests something else to think about once they go home to wash off the ketchup.

Note: Don’t bother pulling this on anyone you could imagine wanting to sue you. In fact, none of these projects are meant for neighbours inclined toward litigation. People go to court over lesser offenses than blue pee.

The new edition of Backyard Ballistics shows how to make a dry-ice powered PVC cannon, among many other projects. The general idea is to build a water reservoir, add a small amount of dry ice and seal it behind a burst valve—basically, a piece of aluminum foil spread across a PVC pipe union.

Once the dry ice hits the water and sublimates, or reverts to gaseous carbon dioxide, the gas builds up pressure in the pipes. When the burst valve gives way, a soft projectile can be launched with a hellishly big bang. A rolled-up tee-shirt can make good cannon fodder. Plus, if they’re not too scared to come downrange of you, people love catching shirts shot out of cannons. Aim skyward—be safe!

The drawing above shows how you can get a basic start on the design using several sizes of PVC pipe. You can find the complete instructions, along with tips like “do not let dry ice come into contact with your bare skin,” in chapter 7 of Backyard Ballistics, second edition.

This looks like a helium balloon, but the gas inside is definitely not inert. The experiment can be dangerous, so keep it nice and small or you could have a Hindenberg on your hands.

Put on safety glasses and rubber gloves. Take an empty glass bottle, like a wine bottle, and use a funnel to place 6 ounces of hydrochloric acid in it. (If you don’t know what hydrochloric acid is, or where to get it, then don’t try this in the first place. Do the ketchup trick instead.)

Cut up a few small pieces of aluminum foil and drop them into the bottle. See that gas coming off as the acid reacts with aluminum? That’s hydrogen! Carefully place a 5-inch balloon over the mouth of the bottle, and let it fill with the gas until it’s the size of a grapefruit. Tie off the balloon.

Use a long pair of tongs to hold the balloon by its knot. Or, use a clamp to clip the knot to a nonflammable object, like a chain-link fence. Dramatically warn your nervous audience to stand back. Using a long fireplace match (and still wearing your gloves and glasses), ignite the balloon by poking it. You should experience a surprisingly brisant and startling explosion.

To dispose of the acid, keep your rubber gloves on, and pour the contents of the bottle into a toilet bowl or sink. Flush everything down the drain with water.

William Gurstelle, aka @wmgurst, is the author of Absinthe and Flamethrowers, The Practical Pyromaniac, and he contributes to Make and Popular Mechanics magazines. The second edition of his book, Backyard Ballistics, came out in September.

Image credits: Intro. Image by Bonnie McDonough/Gizmodo Shooting Challenge; 1. Image by Serhiy Kobyakov/Shutterstock; 2. Image by jannoon028/Shutterstock; 3. & 4. Bill Gurstelle; 5. Image by Aaron and Jen Judt/Gizmodo Shooting Challenge.