But also imagine if they were filled with solid bone -- our head would be dead weight, we wouldn't be able to hold it erect, we wouldn't be able to look at the world around us.
Imaginați-vă că ar fi făcute din oase solide, capul nostru ar fi foarte greu, n-am putea să-l ținem ridicat, n-am putea să privim lumea din jurul nostru.