to knock out to render someone unconscious
to knock down to hit or knock something, usually intentionally, so that it falls
to clank, clatter used to describe a clattering sound, e.g. such as made by a train travelling over the spots where there's a space between the successive rails
to clank, clatter used to describe a clattering sound, e.g. such as made by a train travelling over the spots where there's a space between the successive rails