I chose the neck of the tortoise to be my mechanism
After the researches, i found out that it has the strongest muscles that make its neck go inside the shell in a "S" shape
This is what happens inside
I made the object with the same mechanism,
A box that represent the shell.
Wooden cubes " the vertebral column of the tortoise"
and elastic bands that represents the muscles
and elastic bands that represents the muscles
And while pulling the elastics bands from behind the box, the wooden shapes go inside in a S shape