Oreo's Buried Treasure

This morning the blond twin dropped an open bag of chocolate chips. She told Oreo not to eat any and he walked away from the mess on the floor. As a reward she opened a new box of dog biscuits. After she gave Oreo his treat, he played with it for a bit before standing by the patio door.
When we let him out, Oreo trotted to the grass with his dog biscuit in his mouth. We watched him play with it for a few minutes before he started digging in the grass. A minute later he dropped the biscuit in the hole and started burying it.
The girls and I stood at the window watching. This was a new behavior for Oreo, who hasn't shown much interest in digging. He took a lot of time pushing the dirt over his buried treasure with his nose and his paws. He patted it down, using his paw like you would use your hand. It was fascinating to watch.
A little bit ago I gave him another dog biscuit just to treat him. He walked around the house with it for a while before walking over to the patio door.  I was on a conference call so I didn't open the door for him. Oreo stood there for a while before dropping the dog biscuit at the door. He walked over to his favorite spot and plopped down.
An hour later the dog biscuit is still sitting there, waiting to be buried in the yard. It fascinates me that he wants to bury these rather than eat these. I with I could ask him why, but his communications skills haven't advanced that far yet.