Aw, shucks, I forgot to mention on of the most important aspects of bluegrass. The tight 3-4 part harmony and laid-back singing style lacking vibrato, requiring a good ear and breath control and no part or voice standing out or dominating the harmony. No one wants to call attention to themselves in bluegrass (except the one singing the melody or a solo part), so that the result is harmonic and fluid. When a group is singing it right, you can't sort out who's singing lead, who's singing bass or tenor. And you know it's good when you break out in goosebumps! Now, that's bluegrass!