Have you noticed how slytherin's often associated with monkeys?
Here are just two of the instances-
* In CoS Salazar's statue is described to look like a monkey.
* In HBP Marvolo's face is a lot like a monkey's...even his arms...

Can this be important?
Also, Voldemort does not carry any of this resemblance even though he's the last descendant of Slytherin.

I think it is in reference to the fact that either purebloods are all inbred . . . ergo gicing them monkey features or that because their opinions and such haven't evolved. :D

hahahaha very funny, though of course couldn't you argue that all people bear some resemblance to apes as we're both primates?