Oh, how the mighty have fallen...
So, according to this article, the severed head on the left you see here is actually a mold of former President George W. Bush. (or, should I say, "!")
In the season 1 episode "Fire and Blood," Joffrey decides to show Sansa the heads he's collected of people she knows and loves. These include the head of her her father, as well as the head of "her Septa," Septa Mordane. In the shot where we are shown Mordane's head, the "random" head just to the left of Mordane's bears the profile of the 43rd President of the United States. Don't see the resemblance? Have a look at the side-by side to the right.
If you watch the video from the original article, show creators Benioff and Weiss confirm this rumor saying "George Bush's head appears in a couple of beheading scenes. It's not a choice, it's not a political statement. We just had to use whatever head we had around." Do you believe them, or do you think they did it on purpose thinking it would be funny?