# Bag of Wonder: The Egg > Look inside a hen's egg for 21 days: a tiny spot, a beating heart, a chick. Then it hatches, all by itself! Peep! A free interactive 3D exhibit for children aged 2 to 6, from Curiosity's Child in Troy, Michigan. - Interactive exhibit: https://bagofwonder.com/look-inside/egg/ - Ages: 2 to 6. The story is pitched at the youngest; the tap cards give older children more to chew on. - Cost: free, with no sign-in, no ads and no tracking. - Works on: phones, tablets and computers, in a web browser. Sound on for the narration. ## What it is How a chick grows inside a hen's egg in 21 days, then hatches: slide through the days, look inside, pull the egg apart and tap any part. Free and narrated, ages 2 to 6. How to play: press play to hear the story (read aloud in Kelly's voice, with the words on screen). Slide the time slider back and forth to see any part again. Slide "Pull apart" to see what is hidden inside. Tap any glowing button for a fact. ## The story 1. Here's a hen's egg, poppets, in a cosy straw nest. The mother hen sits on it to keep it warm. 2. Let's look inside! On top of the yellow yolk, a tiny white spot starts to grow. By day two, a tiny heart is beating! 3. Farmers peek inside by shining a torch through the egg. Look: tiny red lines carry food to the baby! 4. The baby grows a big dark eye. Then a beak, toes and the very first feathers start to grow. 5. The chick turns its head to the air bubble, and tucks the last of the yolk into its tummy, a lunch for later! 6. It pokes its beak into the air bubble, takes its very first breath, and peeps! Then it pecks a tiny hole. 7. With a tiny bump on its beak, the chick chips all the way round and pushes the top off, all by itself! 8. Hello, little chick! It comes out wet and tired, then dries all soft and fluffy. 9. Here's our display table: an egg, the shell a chick came out of, and the chick itself! ## The parts, and what we tell children These are the tap cards, word for word. - **A hen's egg**: A mother hen lays about one egg a day. Eggs from the shop are just for eating: they never grow into chicks. - **Shell**: The shell is made of the same stuff as chalk and seashells. It has thousands of tiny holes, so air can get in and the chick can breathe. - **Membranes**: Two thin, stretchy skins lie just inside the shell. They're the papery skin you see when you peel a boiled egg! - **Air cell**: This air bubble at the round end gets bigger every day. It's where the chick takes its very first breath. - **Egg white**: The egg white is mostly water, and works like a soft water-bed for the chick. The chick drinks it all up as it grows. - **Twisty ropes**: Two twisty white ropes hold the yolk in the middle of the egg. They're called chalazae. They're not a baby, just anchors! - **Yolk**: The yolk is the chick's food, not the chick. Just before hatching the chick tucks the rest inside its tummy, so it doesn't need to eat for about two days. - **The baby chick**: It starts as a tiny white spot on top of the yolk. By day two its little heart is beating, and red lines carry food to it from the yolk. - **Chick**: A chick can peep from inside its egg before it hatches, and its mother clucks back. The tiny egg tooth on its beak, for cracking the shell, falls off a few days later. - **Candling**: Shining a bright light through the shell is called candling. Farmers do it to see the baby's shadow and its red lines without opening the egg. ## Getting the science right What we checked, and the myths we steer around: - A hen's egg takes about 21 days to hatch when kept at about 37.5 °C (99.5 °F). The days on the page follow the Hamburger-Hamilton stages of the chick embryo. - The yolk is the chick's food, not the chick: the chick grows from a tiny spot on top of the yolk, and just before hatching tucks the rest of the yolk into its tummy. - The heart starts to beat at about day 2. The egg white is used up by about day 18. - The two twisty white ropes (chalazae) are anchors that hold the yolk in the middle; they are not a cord or a baby. - The chick only breathes air at about day 19 to 20, when it pokes its beak into the air cell at the round end; before that, oxygen comes in through the shell's tiny holes. - The chick hatches alone: it pecks a small hole (the pip), rests, then chips a ring round the round end and pushes the cap off. The mother hen does not peck it open. - Chicks hatch wet and scraggly and dry fluffy in a few hours. The egg tooth is a hard tip on the beak, not a real tooth, and falls off a few days later. - Eggs from the shop are not fertilised and never grow chicks. Shell colour depends on the hen's breed and tells you nothing about the inside. - The cutaway paintings draw the yolk a little smaller than life, and the shell and membranes a little thicker, so every part can be seen. ## How to use it with children Watch the story once with the sound on, then slide slowly through the days and ask, "What has changed?" At the end, pull the egg apart on the display table and find the air cell, the yolk and the twisty ropes. Ask more than you tell, and let the child drive. Then step away from the screen: look at a real egg on the display table (look, don't crack). Shine a torch through a shop egg in a dark room to see the air cell at the round end. Peel a boiled egg together and find the papery membrane. A few minutes together is plenty. The exhibit is a doorway to the real thing, not a replacement for it. ## Credits and licenses The real scans, maps and photographs belong to their makers, under the licenses below. The words, story and code are Curiosity's Child's. - A hen's egg (Gallus gallus domesticus). The egg is a real 3D scan, [Egg](https://sketchfab.com/3d-models/egg-04c322d857504a80983d4bf4f4b56ba9) by [viae](https://sketchfab.com/viae) ([CC BY 4.0](https://creativecommons.org/licenses/by/4.0/)), lightened a little. The inside of the egg, day by day, the candling glow, the nest, the classroom and Ms Daisy are watercolour paintings Kelly made with Grok, checked against the Hamburger-Hamilton stages of the chick embryo. The chick was made on our own computer from a lifelike Grok picture, with Pixal3D. The display table and the torch are from Poly Haven ([side table](https://polyhaven.com/a/side_table_01), [small plastic torch](https://polyhaven.com/a/small_plastic_torch); [CC0](https://creativecommons.org/publicdomain/zero/1.0/)). Real sounds from Freesound ([CC0](https://creativecommons.org/publicdomain/zero/1.0/), thank you!): [hens in a coop](https://freesound.org/s/870508/) (CHallSmith), [very young chicks](https://freesound.org/s/43380/) (AGFX), [a quiet classroom](https://freesound.org/s/205184/) (justingregoire) - Music-box lullaby made for this page. For grown-ups: eggs from the shop are not fertilised and never grow chicks. ## More on the Garden & Pond shelf - [The Pumpkin](https://bagofwonder.com/look-inside/pumpkin/index.md): From one little seed to a big orange pumpkin. Open it up! - [The Frog](https://bagofwonder.com/look-inside/frog/index.md): From tiny floating eggs to a wiggly tadpole to a big bullfrog. Jug-o-rum! - [The Robin](https://bagofwonder.com/look-inside/robin/index.md): Sky-blue eggs, a baby growing inside, hatching day, and first hops on the lawn. Cheep! - [The Oak Tree](undefined): One little acorn becomes a mighty oak. Watch the seasons change and meet who lives in it! ## About Bag of Wonder A free library of interactive 3D "look inside" science exhibits, made at Curiosity's Child, a licensed home daycare in Troy, Michigan. Secular and science-based; welcoming to all. - All exhibits and how we make them: https://bagofwonder.com/llms.txt - For grown-ups and AI assistants: https://bagofwonder.com/look-inside/about/ - To cite: "The Egg", Bag of Wonder, Curiosity's Child (Troy, Michigan). https://bagofwonder.com/look-inside/egg/