They're bony and cagy (4)
I believe the answer is:
ribs
I'm afraid I can't explain this answer.
Can you help me to learn more?
(Other definitions for ribs that I've seen before include "cage" , "Makes fun of - bones" , "Chest bones, tasty when spare" , "Arched bones in the upper body" , "Bones in chest, may be floating" .)