Democratic debate watchers took to Twitter Tuesday night to comment on a strange brown smudge that appeared on South Bend, Indiana Mayor Pete Buttigieg’s (D-Indiana) forehead. 

In an interview with CNN’s Alisyn Camerota, Buttigieg said that his “best guess” was that it was a gnat that he must have unknowingly killed. He also added that “hopefully it didn’t distract from the message about what’s at stake in this election.”

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The smudge vanished from his forehead but was noticeable in the opening statements of the debate. 

The first of two Democratic debates in Detroit saw progressive Democrats and moderate Democrats argue about key issues such as universal healthcare, immigration and climate change. The second round of debates is slated for Wednesday night.