A hedgehog's spines are not poisonous - they are just hard, sharp hairs made of the same stuff as your fingernails. When a hedgehog gets scared, it rolls into a tight ball with all its spines sticking outwards, so foxes and dogs leave it alone. Inside that ball, the hedgehog is soft and warm.
Hedgehogs come out at night. They have poor eyesight but a brilliant sense of smell and good hearing. They can travel 2 kilometres in one night just looking for food - quite a journey for an animal small enough to fit in a shoebox.
In Denmark, hedgehogs hibernate. When autumn comes, they eat as much as they can to put on fat. Then they find a quiet spot under a hedge or in a pile of leaves, curl up, and sleep right through the cold months. Their heart slows down, their breathing slows, and they barely wake up until spring.
Hedgehogs need help from people. They are getting rarer because gardens are tidier (no leaf piles to hide in), there are more cars on the roads, and there is less wild ground to roam. Many Danes leave a corner of the garden wild on purpose and cut a small hedgehog-sized hole in the fence so the animals can wander between gardens.