A 55-year-old female presents to clinic with complaints of migraines. She states that she gets a migraine headache about once a week with associated symptoms of nausea, photophobia, and phonophobia. Vitals are within normal limits. Physical exam without neurologic deficits. Osteopathic structural examination reveals a normal cranial rhythmic impulse. Vault hold reveals a somatic dysfunction of the sphenobasilar synchondrosis (SBS). Which of the following occurs during flexion of the SBS?