Those guys there are on agreement to only use three deflective moves each by the way which allows for the exercise to become a learning curve.

Like everything there are limits, the best Ive seen was one guy blindfolded, still with these three set amount of agreed attacks allowed though.

Advanced to this is when that folding of the arm becomes an elbow strike and trapping the arm with a pull towards you also has a knee coming up into you with it.

Its an add to exercise by agreement and skill level.

In old times when swords and weapons were outlawed in China by the norths take over of the south. The monks used to learn this chi sao, then extend their arm length with two knives one in each hand 12 inches long with sword guards like a bend sai section on the top of the hilt. The length exact so that you cant cut your own elbow joint when rotating around a sword from inside to outside and the guard like hook out the back of the knives to protect the wrist and also to trap like a hand can. That way all the skills learnt open hand could be transformed to warfare against the sword that only the goverment men were allowed to have.