What happens if higher freq PWM is given as servo input

Has anyone tried giving a 5mS or 10mS (or lower freq - 40mS or 80mS) time period PWM signal to a hobby servo rated to work with a 20mS PWM siglan input...

What I am trying to ask.. Is there any way to give a higher (or lower like 25Hz) frequency PWM input signal to a servo...?

I dont have a servo with me right now or I would have tried it my self.. But Im guessing the servo jitters... If so why..?