I was curious too and looked into it LOL I guess it's when you use and move shadows and colors to convey movement and motion instead of just moving the pixels/parts of a piece.
This piece is so remarkably well done :D
It´s designed to lay in a flat surface. In this project the main reference/competitor was habbo, so all objects that habbo had should be better in some ways. The habbo´s one was a simple jawless skull, so I dacided to make a more detailed one and animated. The subpixel effect was made by reducing the sprites, I would be very hard to achieve in other way.
The name of the file was dificult to decide, It was intended to be "screaming skull" like the mith of same name. But it doesn´t look like to scream, rather chewing something.
It looks "huehue" because it has no lips... it is clearly making "omnomnomnom" 
However... great work! 
(It is a skull laying on a table or something like that, I think... otherwise it should be moving the lower part 
)
hia hia hia hia hia hia hia hia hia hia hia hia hia !