First Lady Melania Trump on Thursday tweeted a birthday card in honor of President Donald Trump’s birthday and Twitterverse, although happy for them, couldn’t help noticing a weird thing on the card.

On close inspection of Melania’s tweeted birthday card, there appears to be a stain on between “Birthday” and “Mr. President”. Nobody could able to find out exactly what the mysterious marking is, but the Twitterverse went nuts in guessing it.

The card that Melania posted is simple: “Happy Birthday Mr. President,” it reads. A presidential seal is also visible on the top of the card. The seal which appears is usually used at the top of communications that come from the president, not to the president, so at a first glance, it seems that Donald was sending himself a birthday card. ‘

The stain- though it is small- has made everyone confused. The card may seem like a physical object, and one might even think that the stain to be roughly the size of the period at the end of a sentence, but the card was made digitally.

The stain appears to be in a brownish-yellow and doesn’t seem to have a uniform shape, nor a uniform distribution of color, but the question remains is: What is it?

Initially, one might think that it’s a stylistic marking meant to give the card a realistic look. But that can’t be it, as the stain is a different color from everything else on the card. Some theorized that it’s a drop of coffee that accidentally fell onto the card, and while that’s possible, the armchair detective work didn’t stop there. One popular theory: A teardrop.