br About the video:br br Bone is a material that has the same strength as cast iron, but remains as light as wood. It's one of nature's most remarkable materials: light, strong, adaptable, and able to repair itself. It takes a lot of energy to break a bone—as you can clearly see in this video. Under a smashing blow from a cleaver, the mineralized collagen structure is ductile enough to absorb the blow and dissipate the stress and strain of the impact by stretching and deforming, rather than breaking.br br But this only works when the molecules in the bone are relatively free to slip past one another on a microscopic scale. If you freeze the bone, the molecules in a bone aren't able to do this; as a result the stress of impact remains concentrated in a small area, which starts a crack that will ultimately fracture the bone.br br Temperature and ductile strength are inextricably linked for all solid materials, not just bone. Normally, under stress and strain, the bonds between molecules in a solid are broken as they slip, bend, and twist; then new bonds quickly reform to shift the stress around. But below a certain temperature—called the glass transition temperature—a solid goes from ductile to brittle because molecules cannot easily slip and slide on a microscopic scale, bonds cannot break and reform, and thus cracks will start and quickly spread, causing the material to become brittle and break.br br For most materials, this critical temperature is so high or so low that we rarely notice materials transitioning from being flexible to being fragile. The glass transition temperature for window glass is over 1022 °F 550 °C, and glass is fragile below this temperature. Rubber, on the other hand, has a glass transition temperature below -98 °F -72 °C; so if you froze a tire in liquid nitrogen you could make it brittle enough to shatter.