There is a difference between the checkout nibble and the dominance bite. The checking out out attention getting nibble does not hurt nor does it leaves any marks. This behavior is ok. In a dominance situation it is more like a bite, and the duck is coming with a lowered head. This can also be combined with a charge or a hiss. This will leave a mark and it is not ok. If that happens then you need to mount the duck to clarify who is boss. To mount a duck you need to put one hand onto the upper neck or head and the other hand onto the back holding the duck down to the ground until it stops fighting. You may have to repeat this until the duck gets the point of who is boss. Some owners will sit on the duck holding the head down. Others will grab the duck, and hold it under the arm and carry it around. I had to do that twice with my boy. Now he is the the sweetest duck you can find. He runs up to me chatting in ducky talk. Who knows what he says. The girls do the same. They all will occasionally nibble my clothes. As the owner you need to differentiate between sweet nibble and dominance bite.