After unscrewing the safety knob, the cord had to be pulled like the BZE.
Instead of a wire being pulled through the friction compound, a striker is being pulled against spring pressure. When pulled far enough, the striker will be released and fires a cap igniting the delay pellet.

My own BZ40's :

The BZ 40 on the right is constructed for use with the Meldebüchse Land and See or the Landungsrauchzeichen.
It was fitted with a double hexagonal nut. All time variations can be found like this.

Information thanks to Roman.