Looking for an easy Halloween science experiment for kids? Turn cornstarch and water into spooky monster goo with this simple activity. It’s a fun way to explore science together using ingredients you may already have in your kitchen.
This mysterious mixture feels firm when you squeeze it, then flows through your fingers when you let go. Is it a liquid? Is it a solid? Has your kitchen been haunted?
Meet oobleck: a wonderfully weird mixture that turns a little Halloween mess into hands-on STEM learning.
How to Make Your Halloween Science Experiment
You don’t need a special science kit to get started. Grab a bowl, a spoon, and the ingredients listed at the bottom of this post. Place your bowl on a tray or washable surface to catch any spooky spills.
- Add 1 cup of cornstarch to your bowl.
- In a separate cup, mix ½ cup of water with a few drops of food colouring, if you’re using it. Green makes excellent monster goo!
- Slowly pour the water into the cornstarch, stirring as you go. Mixing will become harder as the goo thickens.
- Test your mixture. If it’s too runny, add a little more cornstarch. If it’s dry and crumbly, add a little more water.
Your goo should flow slowly when left alone but feel firm when squeezed.
Now comes the fun part! Pick up a handful and squeeze it into a ball. Then open your hand and watch your monster goo ooze away.
The Science Behind Your Monster Goo
Oobleck is a non-Newtonian fluid. That means its resistance to flowing changes depending on how you move it.
When you squeeze or press the goo quickly, the crowded cornstarch particles resist moving past one another. As a result, the mixture feels firm.
However, when you release the pressure or move slowly, the particles move more easily. The goo flows again!
Try explaining it to your child this way: “A quick squeeze makes our goo feel firm. A gentle touch lets it flow.” Then test that idea together.
Turn Your Halloween Science Experiment into a STEM Investigation
The best part of this activity is discovering what happens next. Before each test, ask your child to predict the result.
Try these spooky challenges:
- The monster squeeze: What happens when you squeeze a handful tightly, then relax your hand?
- The slow-motion scoop: Does a spoon move through the goo more easily when you push slowly or quickly?
- The disappearing ball: Can you form a ball? How long does it hold its shape after you stop squeezing?
- The recipe remix: What changes if you add a little more water?
For the recipe remix, add water in small, measured amounts. Test the goo after each addition so your child can compare the results.
Younger children can describe what they feel: sticky, firm, runny, or slippery. Older children can record their predictions and observations.
Small Experiment, Big STEM Learning
This simple activity gives kids a chance to practise skills used in STEM—science, technology, engineering, and mathematics.
Measuring ingredients builds maths skills. Making predictions and comparing results develops scientific thinking. Meanwhile, adjusting the mixture encourages problem-solving.
If the first batch is too runny or too dry, that’s part of the investigation. Encourage your child to suggest a change, test it, and observe what happens.
They’re learning that a surprising result can lead to a new question—and another discovery.
Keep the Curiosity Going with STEM Camp
A bowl of monster goo can spark a big question: “What else can I discover?”
At STEM Camp, hands-on exploration helps campers ask questions, test ideas, and build confidence while having fun.
Registration opens November 2, 2026! Check stemcamp.ca for details and start planning your camper’s next adventure.
Monster Goo Ingredients and Supplies
- 1 cup cornstarch
- Approximately ½ cup water
- A few drops of food colouring (optional)
- A mixing bowl and spoon
- A measuring cup
- A tray or washable surface
Parent tip: Explore together and keep the goo away from mouths and eyes. Food colouring can stain, so protect clothing and surfaces. When you’re finished, scrape the mixture into the garbage rather than pouring it down the drain, where it can cause clogs.
