Grapes?

Why is it that my dog (and most dogs) can chew a stick, chew furniture, chew up underwear, chew leather, your favorite shoes, stuffed animals, their own feet and anything that hits the floor in the kitchen but when a grape hits the ground they look at it, take it in their mouth and then drop it still intact and there it will sit under someone picks it up...

But drop a chicken nugget and it will never hit the floor...