These California mussels huddle together,  hanging on to this rock for dear life.
But if the tumultuous waves should  knock one loose, it's in trouble.
Disconnected and all alone is  a very dangerous place to be.
So, it timidly pokes its foot out  from between two armored shells … and makes this.
A byssal thread: a springy lifeline.
It only takes a few minutes  to make a single strand.
But now the mussel is literally  hanging on by a thread.
It’ll keep going until it's made 50-100 of these  connections - what some call the mussel’s 'beard.'
It uses it to fasten securely to a rock  … preferably next to other mussels.
It’ll even use its foot   to drag itself closer to friends.
And why not?
They make great neighbors.
Sticking together makes it  harder for hungry predators and crashing waves to pry them loose.
Mussels thrive near the shore where waves churn  up food for them to filter out of the water.
If they find a good community … they  can stay glued in place for decades.
Long enough for these barnacles  to start using them as furniture.
So how exactly does a mussel make a byssal thread?
Turns out it has a miniature  thread-making factory in its foot.
It all happens inside this long  groove that works like a mold.
Microscopic glands pour in special proteins which  fuse together to form the core of the thread.
Different proteins surround the core,  making a tough, protective coating.
To anchor the thread to the rock, the mussel  secretes a foamy glue, cementing it in place.
The threads are made of similar  stuff as the tendons in our bodies   that connect muscles to bone –   super strong but also pliable.
The glue it uses to hold on  is more than just waterproof.
It actually hardens in water.
If we could figure out how to make a glue like  that, it’d be a game-changer for medicine.
Especially for uses like mending broken bones  and closing wounds in delicate surgeries.
Like the ones doctors do on  fetuses still in the womb.
Now, with their threads all sorted out the  mussels can finally relax … well mostly.
I mean, you can’t blame them for being clingy.