Come to think of it, it reminds me of Prob Lem's old avatar.
Surely my current one? I only have this one and the Christmas one.
Anyway, I really like Simon's proposed "shocked" variant, even though I also like the existing one as well. The other proposed one with slightly narrower eyes doesn't really look as shocked to me, because it reminds me of Dizzy's idle expression in Fantastic Dizzy for the Mega Drive and Amiga.
Do an image search on Google and you might realize that in many instances of Lemmings box art, they do tend to exaggerate the eyes while de-emphasizing (even omitting) the nose and mouth.
And then there's the other issue - two of the Lemmings art-styles clash, which also makes a possible difference here. In older artwork (circa Lemmings/ONML to Lomax or so), when shown at all, the lemmings' mouths are clearly set fairly far back under their snouts (i.e., they seem to have quite shallow jaws). This is different to the Sony-era art, where their mouths are instead placed virtually at the tip of their snouts (i.e., where you might think a nose would go). The former doesn't really show from a front-view like our smileys employ (you'd need a three-quarters view for that, or for them to tip their heads back a little to show emotion
), and the latter looks anything from incredibly strange to borderline scary depending on what emotion is being displayed. Just some random input from my lore/art-style-watching self.