Imagine aliens. Now stop. The aliens you picture are probably humanoid. Maybe big black eyes.
But what about a truly alien species? Something that looks like an octopus. Or something that has parts in a different dimension? Something that is so damn horrible looking that fear is the only thing you can feel. Even though they want to be friendly.
What do we do then?
Is communication even possible? Seriously. How do you communicate with the horrible unknown?