I love this cover from Galaxy Magazine, in fact I'm a fan of the whole look of the magazine which was less lurid, while still being a little lurid. I mean you had to grab readers somehow. What's great about this image is the way it works: you begin by challenging yourself, what shocking alien proclivity would shock the imagination? The most shocking thing an alien can be is familiar - that flips the script, as it were. This cover makes it very clear, the aliens in SF do not live in a distant galaxy, they are us. Now granted, there's probably a racial component here as well that I'm choosing to ignore. But isn't nice to see the idea made explicit: the aliens are us - in the sense that we often don't know ourselves, or that what we think we know of ourselves we learned from myth and stereotype rather than self-reflection.
I'll bet this cover is by the same artist. Same idea.
And I wanted to include this image, just because it's badass: