Why octopuses don't get tangled up in knots

Even though an octopus' has eight arms which are covered in hundreds of sticky suction cups, they never tie themselves in knots. And a new study reveals why.

Researchers from the Hebrew University of Jerusalem claim that they have discovered octopuses manage this feat with a chemical produced by their skin which temporarily prevents their suckers from sucking, even as the their brains are unaware of what their arms are doing.

Guy Levy, who carried out the research with co-first author Nir Nesher said that they were entirely surprised by the brilliant and simple solution of the octopus to this potentially very complicated problem.

Binyamin Hochner, who had been working with octopuses for many years, added that human motor control system is based on a rather fixed representation of the motor and sensory systems in the brain in a formant of maps that have body part coordinates, but the mechanism is hard to envisage to function in the octopus brain as its long and flexible arms have an infinite number of degrees of freedom.

The researchers observed the notion that octopuses lack accurate knowledge about the position of their arms with the behavior of amputated octopus arms, which remain very active for an hour after separation.

Observations showed that the arms never grabbed octopus skin, though they would grab a skinned octopus arm. The octopus arms didn't grab Petri dishes covered with octopus skin, either, and they attached to dishes covered with octopus skin extract with much less force than they otherwise would.

According to the researchers, the drastic reduction in the response to the skin crude extract suggests that a specific chemical signal in the skin mediates the inhibition of sucker grabbing.

In contrast to the behavior of the amputated arms, live octopuses can override that automatic mechanism when it is convenient. Living octopuses will sometimes grab an amputated arm, and they appear to be more likely to do so when that arm was not formerly their own.

The study is published in the Cell Press publication Current Biology.