My seven year old Boston Terrier has within the last two weeks started behavior of nipping/biting and yelping at bath time. The bathing is routine for her, nothing has changed, i.e. shampoo, timing of bath, water temp, and she has no injuries or rashes as far as I can tell, and no other behaviors has changed. It is a mystery why she is snapping/nipping at my hand, and yelping as soon as I pour the shampoo in my hand and gently begin to massage her with it. There are no injuries, sores or rashes on her body, and I am using the same shampoo I have always used with no prior complaints from her. I can't figure it out. She plays everyday outside and when she is done I have to bathe her because she gets very muddy (and she loves getting muddy) and she is an indoor dog. In the past she has never protested her bath time. She begins this behavior when the shampooing starts.