Which Animal Has Hollow, Sharp Quills That Protect It and Help It Swim? — Porcupinefish Explained for a 6-year-old

That description fits a porcupinefish (a type of pufferfish).

Here it is, step by step, in easy words:

1. The porcupinefish lives in the ocean.
2. If something scares it, the fish drinks in water and puffs up like a little balloon.
3. When it puffs up, its hollow, sharp quills stick out all around its body. The quills make it look big and prickly so other animals won’t try to eat it.
4. The extra water or air it takes in can make its body float differently, so puffing and the quills help keep it safer in the water.

Fun facts: The porcupinefish’s quills are not like a porcupine’s on land — they’re part of the fish’s skin and pop out when it puffs up. Also, some pufferfish can be poisonous, so it’s best to look but not touch.