This drawing exercise was an attempt to create a consistent look in egg-shaped heads, independent of size and perspective. If you study each head and compare heads among each other, you can clearly see I still need a lot of practice. The six heads were drawn in roughly 45 minutes. It was the second batch of drawings for this exercise, and certainly not the final.
The problems are manyfold. You first have to draw an outline, that is consistent with the egg form. This means you need to have a mental picture of the 3D shape. Then you have to put in the features (eyes, nose, mouth, etc.), which have to look consistent when comparing left and right side of the face. And third you have to make the expression consistent in all the faces, which also requires a mental picture of a curved plane with the features place on it. Remember, this is illustration, so sometimes the image has to modified slightly from the mathematically accurate three dimensional form. Clarity is generally more important than an accurate and realistic depiction.
All three things have to be done more or less simultaneously, requiring full concentration of an artist who still has to learn all this.
That is all.