The Spanish ribbed newt Pleurodeles waltl shows a bizzare defensive mechanism against predators. X-ray analysis before and after a simulated threat shows that this newt rotates its ribs anteriorly. The maximum measured angle to which the ribs moved was 65 degrees. This forward movement causes the sharply pointed rib tips to lacerate the body wall and project freely from the sides of the trunk as spines. Light microscopy shows the microanatomy, and computed tomography shows the 3D morphology of these unusual weapons. They are 'spear-shaped' and hollow proximally, massive distally and are connected to the corresponding vertebra by a well-developed, two-headed joint. The skin in the penetration areas lacks permanent pores through which the ribs could be projected and is pierced de novo by every antipredator posturing. This investigation provides new insight into the functionality of a highly complex, integrated and unusual defensive strategy.