Nuthatch Sizing up the Seed

I have yet to figure out exactly why it does this, but the nuthatches notoriously come to my feeder and pick through several seed (usually grabbing one, tossing it onto the ground, grabbing another, etc.) before finally selecting one that it wants and flying away. Are my seeds bad? Is it looking for a particular seed (size, weight?) Did it simply not get the kind of grip that it was hoping for the first time, so it lets the seed go so that it can grab another and try again?

Hmmm....

Thanks for stopping by!