I hate to tell you this, but some dogs just don't "get it." Gracie (the Great Dane) never, ever got it. She didn't understand about catching balls or Frisbees either, so we finally stopped "throwing things at her" for fear of getting called in for dog abuse. If we carefully tossed a piece of food, it would likely bounce off her snout, land on the ground, and then we'd point to it and say "Gracie! Treat!" And she's be all surprised ...

So, she wasn't a rocket scientist - she was still a great - and greatly loved - dog.