In pictures: Sex
Some more amazing images from episode 6
A dropped 10kg weight exerts the same force as two bighorn sheep smashing together.
A selection of domestic sheep skulls
We tested the same force of bighorn sheep smashing together on these smaller skulls.
Skull smash: before impact
The impact force on the domestic sheep skull is the same as bighorn sheep colliding.
Skull smash: the aftermath
The impact of the weight on the sheep skull smashed it into many small pieces.
When bighorn sheep clash heads the force is like a baseball bat hitting a baseball.
Ben with a gorilla skull
Gorillas are our second closest related species after chimpanzees.
Over 80% of all mammals have a penis bone and they come in a vast array of shapes.
The walrus has the largest baculum, or penis bone, on Earth.
Male babirusa tusks grow throughout their life and can sometimes pierce their own skull.
The canines of the mandrill, the world’s largest monkey, are larger than those of a lion.