Long ranged dragonfart help

When learning the long ranged version of the dragonfart move, you are required (on the pc) to hold the A and D buttons.  When done so, nothing happens, I fail the spell, and Cartman insults me a bit before redoing the spell.  

Is this a glitch with the pc version?  Or am I just stupid?

The "Cup a Spell" fart is a little confusing.

There's an oval that shows the status of your rumbles.

Look for the arrow around the oval.

A and D moves the arrow back and forth around this oval, use A or D to go around the oval to find the sweet spot where it rumbles.

When you've found it, try to keep it rumbling until the time is up.

 

The tutorial makes it seem like you need to steadily alternate keys, this is not the case.

Thanks Bazgrim.  Figured it out. 

I'm confused how to release it. I can move the arrow until it hits the sweet spot, the whole time I'm holding the left button. If I keep holding either D or A, the arrow will continue to move around the oval.

 

So, once I get the arrow to the far right side and it starts to rumble, I'm still holding down the left button, do I press right and left simultaneously? Am I supposed to quickly switch from left to right? I'm confused.

Never mind, I finally figured it out.

These tutorial sections would be the worst thing about the game so far for me.