After 30 minutes of enjoying his salad at the University of Maryland’s South Campus Dining Hall on Wednesday, Ngou Yin Yip realized that all was not as it seemed.

“I felt something hard, so I stopped chewing immediately,” the sophomore computer science major said.

Among the diced tomatoes and cucumbers, cheese, olives and dressing was the head of a nail. He had no way of telling exactly where the “metal thing” came from.

“It could’ve chipped my tooth or cut me, so it’s very unsafe,” Yin Yip said.

[Read more: UMD students can now leave anonymous comments for Dining Services]

So Yin Yip took to Twitter.

“Apparently the dining hall now serves metal,” he wrote in a tweet to both The Diamondback and Dining Services.

In response to the message, Dining Services spokesperson Bart Hipple tweeted that his team “would like the opportunity to investigate further” and invited Yin Yip to contact him.

[Read more: Four new dining plans will be available to UMD commuter students next year]

In an email sent to Yin Yip, Dining Services apologized for the incident and pledged to do its best to prevent a similar situation from occurring in the future.

“We cannot identify that specific piece of metal you found in your salad,” the email read. “It may be from a piece of machinery, from packaging or may have arrived inside a box of produce. We are checking all our kitchen equipment and will look carefully at our supply chain.”

Hipple wrote in an email to The Diamondback that Dining Services works “to prevent incidents like this, to take responsibility for the rare times they happen, to investigate, to educate our staff, and to continue to be vigilant.”