A Dog’s One Ear Up One Ear Down

It's adorable I know that, but I wonder why?

I know there are some dog experts out there.  Do you know why my little Taffy has this craziness.  The weirdest thing, too is the fact that there's hardly any hair on the ear that just stays up and doesn't move.  It's a part of her personality and I love it.  But I hope it doesn't hurt her.  I do notice when she gets angry the ear goes down, but then pops right back up.  Just a little "why" moment?

Do cats have this one ear up one ear down..or is it just in dogs?  Do you know why?