Former LEGO designer and YouTuber Tiago Catarino takes LEGO building seriously. So when he got comments from people calling his builds “illegal,” he took it personally and sets the record straight.

Illegal builds can be hard to identify, even for the experts who work on model stability, element design, and quality checks on the sets in Denmark. If you notice gaps between bricks or a connection that won’t stay together, those are obviously illegal. Others are harder to catch, like if the LEGO logo on a stud is rubbing against the brick stacked on top and many involve the Technic bricks, which are characterized by circular holes on their vertical face.

Learn more from Tiago Catarino on his YouTube shorts channel, Instagram, Twitter, Facebook, and TikTok.