Update 4 4 vertical vector field

4-4-vertical-vector-field.md

@@ -48,6 +48,7 @@ You can control the size and location of the plane by using _Rendering Pane_ onl
   2. double-click one of the corners of the plane, to reveal the control handles,
   3. drag the control handles to change the size and location of the plane. 
 
+![](img/4-4-1-glow-animation.gif)
 
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