I had an experience similar to this today. For those of you who aren't familiar with Pavlov's dog. This guy named Pavlov conducted an experiment with his dog. Every time he'd ring this bell he'd feed his dog. Ring the bell, feed the dog, ring the bell, feed the dog. It got to the point that the dog would begin to salivate at the sound of the bell.
Well, Lydia has really started loving this game we play with her. One of us will hide and crawl out and chase her and then tickle her. She loves it. She laughs and crawls to the other one in the room to save her. It's like we're "base" or something. Anyway, so she and I were sitting in her doctor's office today waiting for her doctor to come in. She was sitting in the middle of the room playing when all of sudden we heard thumping in the hallway (someone was walking.. rather loudly.. down the hall). To her it sounded like someone was crawling towards her.. haha. So, she stops playing, starts laughing and crawls to me as fast as she could. I picked her up and she stared at the door just waiting for daddy to crawl in and start tickling her. lol. She just stared at the door with a smile on her face. It was so funny. Of course, daddy never came in. It still makes me laugh thinking about it. She's so fun :)