What's up with that dog?

Pepper, aka The Voodoo Queen, did something odd the other night. Being half Border Collie, doing odd things is not out of the norm but this sort of threw us. Pep was sitting on her couch (Yes, she has a couch, it's falling apart and no once else can sit on it, and we can't affort new furniture). Hubby and I were talking and suddenly she nodded her head vigorously. It only lasted a second, but it was very odd. She hasn't done it since. She's fine, no seizure or weakness. Just that head nod.