She hadn't eaten the yarn.
She had eaten the chocolate.
For those of you who haven't heard, chocolate is toxic to dogs. I had never looked into how much was needed to cause problems, because I just assumed that by NOT feeding chocolate to my dog, I wouldn't have any issues.
So I panicked a bit. Luckily, I have Colby to turn to for advice, and she assured me that one piece of milk chocolate was not enough to hurt Mia. Might upset her tummy a bit, but it wouldn't hurt her.
If I react like this with my dog, it's a really good thing that I don't have kids!