Aha! so that is what they do. I see, thanks jae! Maybe if I filled it with something really succulent like PB he would do it, I'll give it a try.
I stuff marrow bones too after he's cleaned them out. It doesn't take him very long to get the PB or cream cheese out though. At this time the marrow bone is his favorite and keeps him occupied the longest, and he gets a new one every couple days.
OK, off I go to stuff a kong.