Very impressive, but it has also some limitations, the softmax output that shows the confidence is often unreliable (tested empirically). This is an example of misclassification that has a score of 99%: https://imgur.com/a/wnr8K
The reason we find the frown to be most important is our understanding that this is a common symbolic representation of an emotion.
If we were to look at it as just an abstract shape, I think we'd come to the same conclusion as the algorithm though.
:) :( :| :O :D :/ ;)