This animation shows a paraboloid being changed into a saddle.  The trick, of course, is to study the animation and figure out why it works.  Enjoy! 

>	with(plots):

>	animate3d(x^2+cos(t)*y^2, x=-15..15, y=-15..15, t=0..2*Pi, frames=40, orientation=[58,86], lightmodel=light1);

 

 

>