Animation based on MRI data of a chick inside its egg. Initially there is a series of 2D MRI scans showing the chick curled up inside the egg, which is then used to build a 3D model. The scan shows the chick at day 17 of its 21-day incubation period. The animation in the last part of the clip shows the full-term chick. When the chick is too large to breath just the oxygen that diffuses through the shell, it uses an egg tooth on its bill to break through first the membrane surrounding the egg's air sac, which supplies it with a little more oxygen. Low oxygen levels then subsequently cause the contraction of a strong muscle in its neck, which causes it to repeatedly peck the shell with its egg tooth, breaking through the shell of the egg itself. The egg tooth is lost shortly after hatching. This scan data was acquired at the UCL Centre for Advanced Biomedical Imaging (CABI).