The pentatonic scale is a really popular tool for improvising because it leaves out the 9th and the 6th, which are two tones that can be easily miused and sound bad. The 1st, 3rd, 4th, 5th, and 7th go with almost every chord in A Minor. It's almost hard to sound bad when using the pentatonic scale (as long as you're in the right key). Also, the pattern is really easy to remember.
"You must stab him in the heart with the Bone Saber of Zumacalis... well, you could stab him in the head or the lungs, too... and the saber, it probably doesn't have to be bone, just anything sharp lying around the house... you could poke him with a pillow and kill him."
- Aqua Teen Hunger Force, The Universal Re-Monster