From HowStuffWorks.com:
Both King Charles I and Queen Anne Boleyn are reported to both have showed signs of trying to speak following their beheadings (by executioners’ swords, rather than by guillotine). German researcher S.T. Sommering cited reports of decapitated heads that have ground their teeth and that the face of one decapitated person “grimaced horribly” when a physician inspecting the head poked the spinal canal with his finger.
Perhaps most famously was the study conducted by a Dr. Beaurieux in 1905 of the head of executed criminal Henri Languille. Over the course of 25 to 30 seconds of observation, the physician recorded managing to get Languille to open his eyes and “undeniably” focus them on the doctor’s twice by calling the executed man’s name.
It makes sense to me that you could move your tongue, jaw and eyes after a guillotine or sword beheading. The brain would still be receptive to a touch on the spinal canal and I think you would be receptive to auditory sounds also. Only when the loss of oxygen in the blood cells went too far down would the brain shut down.