Animals and Robots.

Vulnerability is humanity, though. Allowing yourself to truly be who you are when you don't think anyone is watching, or letting your guard down around someone who you believed has earned it, is allowing yourself to be vulnerable. Trembling hands and frozen tears and telling your waitress the exact way you like your coffee with the same bitterness in your voice as the taste in your mouth are all examples of being human, showing that you're someone deeper than what you portray as yourself.