Legos haven’t just become astronomically expensive in the past 35 years. According to a new study from researchers in New Zealand, the popular kids’ toys have also developed a bit of an attitude problem.

Lego characters released since the early ‘90s are proportionately more angry, the study found. Authors of the study hypothesized the spike in negativity could be related to the release of more thematic Lego sets, such as pirates or “Harry Potter,” which include weapons and minifigures representing “good guys” and “bad guys.”

“It is our impression that the themes have been increasingly based on conflicts,” wrote the three researchers Christoph Bartneck, Mohammad Obaid and Karolina Zawieska. Two of the authors work for the University of Canterbury; the third is from the Industrial Research Institute for Automation and Measurements.

Researchers arrived at this conclusion through a meticulous scientific process, which reads as almost comical given their subject matter. After cataloging and photographing the 3,655 Lego characters released between 1975 and 2010, they asked 264 American adults to characterize the figures’ expressions as angry, happy, sad, disgusted, surprised or fearful.

Researchers then processed those numbers and plotted them on graphs like the one below, which illustrates the proportional growth of angry faces since the early ‘90s. Variables (like skin color and whether the figure’s head is attached to a body) don’t substantially throw off their conclusions.

That’s pretty alarming in a world where chewing a Pop-Tart into a gun shape is grounds for school suspension, and the psychological impact of violent video games remains a hot debate. One would predict that conflict-oriented figurines are the last thing parents want in their kids’ toy chests. In fact, the researchers themselves sound concerned about the implications for child psychology:

“We cannot help but wonder how the move from only positive faces to an increasing number of negative faces impacts how children play … The children that grow up with LEGO today will remember not only smileys, but also anger and fear in the Minifigures’ faces.”

But before you confiscate your kids’ Legos, consider the good that even angry Legos can do. The study’s authors acknowledge that a range of emotional expressions “connect[s] to the complex interaction scenarios of today’s users” — in other words, the variation mirrors real life, where anger, fear and “smileys” all magically coexist. And some child psychologists have suggested that conflict-driven games, even those with toy weapons, help kids grapple with issues like “the struggle between good and evil,” a point made by George Washington University’s Jonathan Turley in a controversial 2011 op-ed.

In either case, Lego does still sell boring old building blocks. They may lack flashy movie tie-ins — Hobbit Legos, anyone? — but experts agree they’re still great for kids.