Insert the hook through the loop of the next chain stitch, yarn over the hook and draw the hook through the chain stitch you now have two loops on the hook.
Yarn over hook and pull through both loops.
Punto bajo (pb)/ Maille serrée(m.s.) /Feste Masche (fM)/ Maglia Bassa (m.bassa)/ Ponto baixo (pb)/ Oczko scisle / Kinnissilmus-ks