Is it healthy/normal to feel bad after killing vermin?

Today I, in a moment of joviality, threw a rock at a chameleon which proceeded to crush its neck and end its life. To my consternation, a rush of grief and remorse overwhelmed me. I don't really understand why I'm upset by this. Not more than a month ago I set fire to a writhing toad doused in alcohol. The only feeling at that time was amusement because I felt only disgust towards that slime ball. Being a man of utmost manliness I should have no qualms about killing the way cavemen used to. Needless to say, I'm a watered down version of the pentagon of manliness that is cavemen since I kill only cold blooded creatures. If there is any psychiatric expert out there,could it be possible this event is merely a trigger for releasing withheld stress?