Aliasing eyebrows → invalid_tag
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Reason:

Eyebrows are visible in most posts here but severely undertagged, and it doesn't seem to be of much use as a search term.

Of course, we could just encourage people to use the tag more often instead. In that case, there are tags like raised_eyebrow and eyebrow_piercing that could be implicated to it.

About the only use I could think of for that tag would be to move the relevant ones over to something like non_mammal_eyebrows but I doubt anybody wants a tag like that.

Meh, probably. I'll create a placeholder for this in the meantime.