anosognosia . She would have her arm lying in her lap and when asked who the arm belonged to, she would reply, "that is my mother's arm". She literally believed that it was not her arm. Now that is some whack shit, and I'm not even sure how that article discussion progressed to the next bit, but it did. (I highly recommend you read the linked article it is messed up)
Amanda and I started to blame all bad behavior on our "mother's arm".
-I had one too many drinks last night and my mother's arm drove home.
-This weekend my mother's arm made me french kiss the bartender.
-Why do I have a scab on my cheek? My mothers arm smoked marijuana cigarettes, made me ride my bike and I fell down.
Mother's arm is a fickle mistress.* One never knows when it will rear it's dismembered digits and get you into trouble, although the arm is generally coaxed out with alcohol or drugs. When it does indeed come out, it's always a great story covered in humiliation. The upside is you have a perfect explanation for every naughty thing you do.
* That is an Amanda-ism