In Cap. X of LLPSI, Ørberg introduces these three sentences:
Cum avis volat, alae moventur.
Cum homo ambulat, pedes moventur.
Cum piscis natat, cauda movetur.
While I understand the general meaning of each, the use of cum and passive verb make it a little more challenging for me.
I think that each more or less means something like:
With wings the bird flies.
With feet the person walks.
With a tail the fish swims.
Is this correct, and is it just the placement of cum at the beginning of each sentence and use of comma that are making it more confusing for me? Shouldn't wings, feet, and tail be ablative?
Is he introducing cum as an adverb, so it would be when a bird flies, the wings move?