Both of these pairs of slippers can be found at NEXT stores in 2010. The difference is, the original design (left) could be found early in the year, and the new winking design (right) found later in the year. It's unknown why they quickly replaced one pair with the other. The originals were also released in the USA by GE Entertainment.
There are several things to note about the pairs...first being that the 2nd ones include a bit of the chest/belly dot while the originals do not, also, the 2nd pair has an open mouth/grin expression, while the first is just the side-smile. The ears and spikes look the same. Also notice you can see the texture where the 'eyelids' are to have met in the middle. While the construction looks decent on both pairs (rather plush-like) it's still an odd concept to be wearing Sonic's heads on your feet.