my blender doesnt extrude the way it does in your video. when i select an edge to extrude it only extrudes that edge. th...

my blender doesnt extrude the way it does in your video. when i select an edge to extrude it only extrudes that edge. the rest of the mesh doesnt adapt to it as you see in this lesson between 1:20 - 1:30 . whats going on?