I think, it's showing the "harshness" of each of them...sort of as a warning..."if this is you, beware of beheading (biting the heads off) those around you."
Men can be too harsh, and "kill" the more sensitive ones around them. Women too, can be too harsh. It's mainly your TONGUE that does it, and the toungue is the sword of the body. Our sWORDS can lash out and really hurt people, especially if we are rash, and we need to govern this aspect of ourselves. Our Intellects can do this to our hearts, as well.
The King of Swords, while being a fierce warrior and strong, brilliant, and charismatic leader, on the negative side, can be biting, careless...This holds true for the Queen as well, strong, intelligent, willful... but on the negative, controlling...a "shrew".
I think the cards, if upright, in displaying the heads, can be showing a little of their dark side, as a "warning" or object lesson against going too far and becoming this way...if reversed, they are saying that it has gone too far and become this way.