My lab goes absolutely nuts over empty bottles. I dont know how he does it but he can be asleep across the room and can tell when I take the last drink out of a bottle. I dont know if he hears a difference in the cap twisting off or on but he is right at my feet waiting for me to take the last drink. I buy all kinds of toys but he will go for a pop bottle every time. He chews the cap and little plastic ring under the cap off and shreds the label. I wish I was so easy to entertain sometimes.
