Ducks try and eat anything they can get in their mouths including fingers and toes.  I have a native cherry that drops small hard berries -- a little fruit round a large stone -- in the fall.  My ducks still pick them up and try and eat them: they don't seem to have realized that they are not edible by ducks!!!
But when it comes to plants and weeds, they quickly develop favorites and then leave everything else alone until their favorite is done. They demolished lilies I had, but at the moment are ignoring the new shoots growing back.  They seem to like ferns but I have some lush weeds that I let grow as ground cover, and the ducks don't touch them. They like my vegetables/salad crops but are too lazy to get up onto my raised beds to eat them..
But my ducks like to play nibbly nibbly with me -- it's not biting, although I only have one duck I trust not to bite my nose, and doesn't hurt. They will nibble my clothes: my sleaves, my hems, my shoes, my zips.  I think its affection, but as I already noted, I only have one that I allow to nibbly nibbly by my shoulder as she is the only one I trust not to bite my nose (and ear).
So yes a bit like a puppy.
When I was replacing the roof on my son's duck house two weeks ago, I had to count every screw and make sure they were accounted for as a 1 inch screw could easily go down a ducks throat and cause serious trouble.  Ducks are very inquisitive [aka nosy] and my son's were round my ankles the whole time I was working in the garden, nibbling around my tool box and even my drill when I put it down.  They aren't put off by power tools.  I have one -- the trustee -- who was up behind my husband pulling on his shorts when he was using a pole chain saw in our garden.
So, take care of your little lovelies and be aware that they are into everything and put everything in their mouths