collision detection: Narwhal tusks

Narwhal tusks: Delicate sensing organs?: "This violates all known tooth anatomy"

Isn't the net great!
The close-ups showed that 10 million nerve endings tunnel from the tusk's core toward its outer surface, communicating with the outside world. The scientists say the nerves can detect subtle changes of temperature, pressure, particle gradients and probably much else, giving the animal unique insights. "The tusk is not about guys duking it out with sticks and swords."