Choose the correct answer.

Emperor penguins are amazing birds and great parents. They can’t fly, but they can swim really well. Every winter, the mother has one egg and gives it to the father. Then she goes to the sea for food. It’s very cold, so the father keeps the egg warm on his feet. He stays with the egg and doesn’t eat. After two months, the baby comes out of the egg. Soon, the mother returns with their food. The father can leave for food now.

The father keeps the egg _______ on his feet.