Scarlett Johansson's alien character, driving around Scotland in a van, is on a metaphorical journey as well. With each encounter, each stop, she acquires a human trait of increasing complexity, from shallow chit-chat and filling survival needs through group behavior, humor, pity, empathy, mercy, love, and fear.
Along the way she is shadowed by her patriarchal alien overseer who seeks to set boundaries on her development. The point at which he intervenes is telling, and the alien "She" ditches her van and overseer to learn more. In the process she shows more humanity than many of us can muster.
"Under the Skin" is beautifully crafted but difficult to watch. The opening "birth" sequence and scenes around Scotland are gorgeous, but there are several heart-rending scenes, and the demise of some characters is visually arresting. Those watching for prurient reasons or who are unwilling to put some thought into it will be disappointed. The pace is Kubrickian and, like "2001: A Space Odyssey", what little dialog there is is largely meaningless in terms of plot.
I am not particularly a Scarlett Johansson fan, but her acting is superb here. Her ability to communicate complex emotions through expression and body language alone is striking. The other characters are well-portrayed, but, truthfully, Jonathan Glazer's direction and Johansson are all that really matter here.
In the end, this movie challenges us to think about what is under our skin. Inside ourselves we will find predator and lover, callousness and vulnerability, victor and victim. But in what proportions?