A continuing bilingual series explaining interesting, counterintuitive and commonly misunderstood questions in mathematics, physics, chemistry, biology and physiology.
- Does a Mirror Really Reverse Left and Right?
- Does Adding Salt Really Make Water Boil Faster?
- Why a 10% Increase and a 10% Decrease Do Not Cancel
- Is Water Really ‘Thrown Out’ During a Washing Machine Spin Cycle?
- If Oil and Water Don't Mix, How Does Soap Remove Grease?
- Why 23 People Are Enough for a Shared Birthday
- Why a Shared Birthday Is Likely Among Just 23 People
- Why Does a Group of 23 Make a Shared Birthday More Likely Than Not?
- Why Does a Bathroom Mirror Fog Up?
- Why Does a Candle Flame Point Upwards?
- Why Can’t a Chessboard with Two Opposite Corners Missing Be Tiled?
- Why Does a Chopstick Look Bent in Water?
- Why Does a Compact Disc Show Rainbow Colours?
- Why Can’t a Cracked Knuckle Pop Again Immediately?
- Why Does a Hiccup End with a Sudden ‘Hic’?
- Why Can a Hot Road Look Covered in Water?
- Why Does a Lake Freeze from the Surface Down?
- Why Does a Metal Spoon Get Hot Faster Than a Wooden One?
- Why Does a Half-Twisted Paper Loop Have Only One Side?
- Why Does a Raw Egg Start Spinning Again After You Stop It?
- Why Can Staring at Red Leave a Cyan Afterimage?
- Why Does a Rice Cooker Switch to Keep Warm Automatically?
- Why Can’t a Round Manhole Cover Fall Through Its Own Opening?
- Why Does a Balloon Stick to a Wall After Being Rubbed on Hair?
- Why Does a Sealed Snack Bag Puff Up at Altitude?
- Why Does a Shuffled Deck Almost Never Repeat an Order?
- Why Does a Spinning Coin Wobble Faster Just Before It Stops?
- Why Is Your Face Sometimes Upright and Sometimes Upside Down in a Spoon?
- Why Does a Straw Look Bent in Water?
- Why Can a Suction Cup Hold Until Air Leaks Under Its Edge?
- Why Does a Vacuum Flask Still Slowly Cool Down?
- Why Can a Wet Finger Make a Glass Sing?
- Why Does A4 Paper Keep the Same Proportions When Folded in Half?
- Why Does Alcohol Feel Cool on the Skin?
- Why Does Aluminium Foil Have a Shiny Side and a Dull Side?
- Why Can an Eraser Remove Pencil Marks?
- Why Can an Overcooked Egg Yolk Develop a Green Ring?
- Why Can an Unridden Bicycle Stay Upright for a While?
- Why Is a Round Trip’s Average Speed Not the Simple Average?
- Why Does a Bathroom Mirror Fog Up?
- Why Do Both Pupils Constrict When Light Enters One Eye?
- Why Does Bread Stale Faster in the Fridge?
- Why Does Bread Turn Firm as It Goes Stale?
- Why Can Breath Cool Hot Soup Yet Warm Cold Hands?
- Why Do Bruises Change from Blue-Purple to Green and Yellow?
- Why Are Bubbles in a Foam No Longer Round?
- Why Do Cats’ Eyes Shine in the Dark?
- If Every Fourth Year Is a Leap Year, Why Isn’t 2100?
- Why Does Chalk Squeak on a Blackboard?
- Why Chilli Feels Hot Without Raising the Temperature
- Why Can Chocolate Develop a White Bloom?
- Why Does Cold Skin Break Out in Goosebumps?
- Why Does Copper Slowly Turn Green Outdoors?
- Why Does Coriander Taste Soapy to Some People?
- Why Do Cut Apples Turn Brown?
- Why Cutting Onions Makes You Cry
- Why Does a Drop of Dishwashing Liquid Make Pepper Rush Away?
- Why Is Division by Zero Undefined?
- Why Does a Dried Coffee Drop Leave a Dark Ring?
- Why Do Your Ears Pop During a Flight?
- Why Can Eating Ice Cream Too Quickly Cause a Sudden Headache?
- Why Does Egg White Turn from Clear to White When Heated?
- Why Do Our Eyes Need Time to Adjust to Darkness?
- Why Do Fingers Wrinkle After Soaking in Water?
- Why Do Fingers Wrinkle in Water?
- Why Are Four Colours Enough for Any Planar Map?
- Why Can Fresh Pineapple Stop a Gelatine Dessert from Setting?
- Why Isn't Frost on Grass Simply Frozen Dew?
- Where Does the ‘Metallic’ Smell on Your Hands Come From?
- Why Does Hard-Water Tea Form a Film on Its Surface?
- Why Does Heated Milk Boil Over More Easily Than Water?
- Why Does Heated Milk Form a Skin on Top?
- Why Does Honey Crystallise in the Jar?
- Why Are Honeycomb Cells Mostly Hexagonal?
- Why Can Hot Glass Crack When It Is Cooled Suddenly?
- Why Can Hot Water Freeze Before Cold Water?
- Why Do Ice Cubes Crack When Dropped into a Drink?
- Why Do Ice Cubes Stick to Damp Fingers?
- Why Ice Floats on Water
- Why Identical Twins Still Have Different Fingerprints
- Why Does Ketchup Flow More Easily When Squeezed?
- Why Do Many Leaves Have More Stomata Underneath?
- Why Do Mature Sunflowers Usually Stop Following the Sun?
- Why Microwave Ovens Often Heat Food Unevenly
- Why Does Mint Feel Cool Without Lowering the Temperature?
- Why Do Oil and Water Separate Again After Shaking?
- Why Does One Nostril Often Feel More Open Than the Other?
- Why Can a Paper Towel Draw Water Upwards?
- Why Can Peeling Clear Tape Produce Flashes in the Dark?
- Why Do Pine Cones Close When Wet and Open When Dry?
- Why Might a Computer Say 0.1 Plus 0.2 Is Not 0.3?
- Why Does a Popcorn Kernel Suddenly Turn Inside Out?
- Why Can Water Boil Above 100°C in a Pressure Cooker?
- Why Does Rain on Dry Soil Release an Earthy Smell?
- Why Don't Raindrops Keep Accelerating as They Fall?
- Why Do Raindrops on Glass Suddenly Slide After They Merge?
- Why Random Arrivals at a Bus Stop More Often Land in Long Gaps
- Why Do Raw and Boiled Eggs Spin Differently?
- Why Does Red Cabbage Juice Change Colour with Acids and Bases?
- Why Can Pressing Closed Eyes Produce Flashes of Light?
- Why Does Salt Make Ice Melt?
- Why Does Salt Melt Ice but Stop Working in Extreme Cold?
- Why Does Shaken Soda Spray When Opened?
- Why Can Shoelaces Suddenly Come Undone While You Walk?
- Why Must Six People Include Three Mutual Acquaintances or Three Mutual Strangers?
- Why Can a Tiny Paper Cut Hurt So Much?
- Why Do Soap Bubbles Show Rainbow Colours?
- Why Can Soap Carry Away Grease That Water Cannot?
- Why Does Soap Lather Poorly in Hard Water?
- Why Does Sparkling Water Sting the Tongue?
- Why Can Spinning an Egg Reveal Whether It Is Raw or Cooked?
- Why Can Stainless Steel Still Rust?
- Why Do Stars Twinkle More than Planets?
- Why Do Still Rocks Seem to Rise After You Watch a Waterfall?
- Why Does Super Glue Bond to Skin So Quickly?
- Why Can Water Below 0°C Freeze When Disturbed?
- Why Do Tea Leaves Gather at the Centre of a Stirred Cup?
- Why Does the Body Shiver in the Cold?
- Why Is the Edge of a Shadow Often Blurred?
- Why Doesn't the Eye's Blind Spot Look Like a Hole?
- Why Does the Moon Look Larger Near the Horizon?
- Why Does the Room Still Seem to Spin After You Stop Turning?
- Why Is the Daytime Sky Blue but Sunset Red?
- Why Does Toast Turn Brown and Smell More Aromatic?
- Why Do Tree Rings Vary in Width?
- Why Does Multiplying Two Negatives Give a Positive?
- If Blood Is Red, Why Do Veins Look Blue Through Skin?
- Why Can Vinegar Remove Limescale from a Kettle?
- Why Does a Warm Sparkling Drink Go Flat Faster?
- Why Can Warm Water Make a Metal Jar Lid Easier to Open?
- Why Can Water Boil Below 100°C?
- Why Water Often Gets Noisy Before It Boils
- Why Do Wet Clothes Dry Faster in the Wind?
- Why Does Wet Fabric Look Darker?
- Why Does Paper Tear More Easily When Wet?
- Why Does Wet Pavement Look Darker?
- Why Can Wet Sand Build a Castle While Dry Sand Falls Apart?
- Why Do White Clothes Glow Blue Under Ultraviolet Light?
- Why Does Wilted Celery Become Crisp Again in Water?
- Why Can Seeing Someone Yawn Make You Yawn Too?
- Why Can Yeast Make Dough Rise?
- Why Does 0! Equal 1 Rather Than 0?
- Why Does 0.999… Equal 1 Exactly?