Now we've got tendons to be harvested from butchered animals,
and the appropriate new means and options within textilecraft menu to process them into sinew yarn.
It's all ready, and it goes like this.

Henrik has managed to hunt down an elk, and has butchered it. Among other parts there are now also elk tendons to be picked up.
And within TEXTILECRAFT menu there's a set of three new options. First of all, the fresh tendons need to be dried in order to process them further.

Henrik got the elk tendons dried and then moved into separating the sinew fibre from them.
This involves pounding the dried tendons on a hard surface until the fibres start to separate.
Hernik has got a tree trunk as a working surface and starts pounding with a spare firewood.

From all the bundles of sinew fibre Henrik separated he can now make 40 meters of sinew yarn.
That's a good amount of self-made sinew yarn for many future crafts and binding needs on his way.

However, for the fishing tackle there's now new kind of yarn requirement added; water-use yarn.
Sinew yarn can't be used for fishing tackle because it weakens and stretches when wet. Luckily Hernik has got
more than enough hemp yarn also to craft a fishing rod.
These are future features - not yet functional in current version 3.86.1.