It’s hot in Japan. Hot enough to melt a dashboard rubber duck into a forlorn pool of gooey plastic. And hot enough to make thousands of people intent on proving or disproving the authenticity of a now-viral tweet. The initial tweet, posted yesterday and already garnering close to 500,000 retweets, depicts a small green duck succumbing to the heat and becoming the flat-faced avatar of humid summer doldrums. It reads “This is the worst, I can’t believe it.