HELP! What does the author mean by “a little cage of bone” ? in the poem "incident in a rose garden"

Read the paragraph many kids do not like to exercise. they do not realize that it is for their own good exercise is good for the body. there are many types of exercise activities to choose from. an activity such as running increases circulation lifting weights builds muscle and strengthens bones playing a sport such as basketball can improve coordination so pick an activity and get your exercisel what is the big picture idea in the paragraph? many kids do not like to exercise exercise is good for the body an activity such as running increases circulation lifting weights builds muscle and strengthens