I have a 14 month old Great Dane mix puppy that is acting strangely. The other day he saw a bag that had blown against a fence on our property and began to bark and growl and act nervous until he got up the nerve to smell it, after which he was fine. He also doesn't recognize my husband and I if we are walking up the driveway instead of driving or if we have hats on. He acts the same way; barking and growling until we speak to him or he smells us. Finally, he seems to notice things in the house suddenly and growl at them until he smells them, then he doesnt care. My feeling is that he can't see well. Any thoughts? He is never aggressive or otherwise "odd", just this. Thanks.