What if he then asked the same question regarding you and the air. Where do you end and the air begin? This time it isn't so easy. The air is not only around you, it sinks into your pores, it enters your nose and down into your lungs. It is in your blood. The air, or at least the oxygen from it, is in every cell in your body. Your body couldn't function without it. If you managed through some miraculous effort to completely separate yourself from the air, you would die.

    And what about the earth under your feet? Can you say where you end and the earth starts? Not really, because much of what makes up your physical body comes from the earth and is therefore part of it. If the planet disappeared from under you, would you still exist without it? Of course not, not in physical form anyway, so you are not truly separate from it, are you?

    And then we have the new concepts of quantum physics, that just happen to match ancient concepts of spiritual people, that everyone and everything is joined together in a way they don't entirely understand, but can scientifically demonstrate, and they call this interconnectedness "entanglement".

    If we started this over again using an advanced spiritual person instead of an average person, things would have gone somewhat different. When the teacher asked him to define where he ended and the dog started, he would know that there was no answer because separation is an illusion. He can recognize dog and tree and earth and sky, but not as things separate from himself and everything else, but as pieces of the whole, the one.