In our old house, we had a doggie door in the garage leading out into the yard. I was out playing with our dog one day, and we were going back into the house. I opened the door to go into the garage. The dog was by my feet. He stopped, looked at the doggie door, and looked at the open door, and then decided to go through the open door.
Nothing instinctive there, it was a purely arbitrary decision to make. He chose the open door, although he could have easily gone the other way.
Why'd he go through the open door? Maybe he thought it looked easier, I don't know.
Regardless, this was a real-time decision that he made. Not a survival instinct or anything, just a choice.