Hi! Sorry for the delay. Your heads look alright, the definition of planes on the first one is spot on. However, when constructing the "helmet", you have to consider that it is a 3D form as well, and so, it should follow the same rules as the rest of your forms. What I mean by this is that the horizontal lines that come from the muzzle should be curves that follow the contour of the sphere underneath. As they are now, they're flattening the drawing. On this head for example, the edges on the upper section of the "helmet" clearly follow the contour of the sphere they're sitting on. Your second cat got that much better.

Another thing is the eyelids. Think of them as masses wrapping around the sphere of the eye. That's the key factor here I think, you're treating your eyes as flat circles instead of spheres. It is tricky, as sometimes the eyelid is minimal. Coming back to Uncomfortable's demos, look at this. You'll see that, while the eyelids do not "wrap" around the eye completely, they do follow its contour in the areas that make contact with it.

Now, for the second cat. The construction is alright, you got the point, which is the important thing here. Here I made another simulation on your model. You can see that the "lip" opens beneath the nose, but then turns the corner (or tries to anyway) and follows the plane of the muzzle. You couldn't do that on your drawing because you got the planes mixed up: we can see a lot more of the front of the nose on your drawing than on the reference. That's alright, but then something weird happened and the lines you ended up making do not sell neither the original plan of your drawing, nor the planes on the reference.

Try to solve that by carefully observing your reference, sometimes you can "trace" it in the air and find the form lying underneath, that way you can measure, more or less, how much of the form we should actually be able to see. And you make a mistake and end up showing more than you should, stick with it and try to make the best out of it, instead of correcting it.

But the thing with the lips not only comes from the weird muzzle, on your first drawing, something similar happened, and the mouth looks a lot more like a cartoon mouth than added forms following the contour of the forms underneath, even though you could do that on that drawing. It is tricky (especially without adding detail, which would carry the sense of volume better, since those forms are so fluffy), but it is doable.

You can see that on the demo I wrapped the forms in the neck and the left eye around the sphere and the muzzle (the eye one could be better if it wrapped around the sphere as well to be honest). That feels more solid than just linking lines to the neck like you did. Think about every form you're adding as a 3D mass, just like we did on the insects. That being said, if I drew the neck, I would've wrapped the mass around the neck and maybe a section of the head sphere, it depends on the context I guess.

That's it I think, you just have to be more careful when observing the reference, and remember to treat every mass as a real thing, make every mass you add follow the rules you've already followed when adding the basic forms.

I think you're ready to move on; you'll have plenty of opportunity to work on those things on your own time, if you decide to do so. So, move ahead to the 250 Cylinder Challenge.