Octopuses can stiffen their limbs to create "trick elbows" or temporary joints. These pseudo joints function in a similar way to human joints. An article on MSNBC.com explains:
Researchers recorded muscle activity in octopus limbs, and found that an arm generates two waves of muscle contractions that propagate toward each other. When the waves collide, they form a part-time joint.
This process occurs three times, forming a shoulder where the arm meets the body, a wrist where the suckers have grasped their food, and an "elbow" somewhere in between. The elbow typically exhibits the most movement during food retrieval.
The researchers say this is a remarkably simple and apparently optimal mechanism for adjusting the length of arm segments according to where the food item is grasped along the arm.
The similarity of structural features and control strategies between jointed vertebrate arms and flexible octopus limbs suggests that these configurations evolved separately in octopuses and vertebrates, a result scientists call an example of convergent evolution.
This isn't the first time we have seen an Octopus doing something extraordinary. Last July we learned that a young octopus could open the lid of a tightly closed jar in less than ten seconds.
Octopuses can stiffen their limbs to create "trick elbows" or temporary joints. These pseudo joints function in a similar way to human joints. An 
