Your interviewer will likely ask you situation- and knowledge-based questions to understand how well you are able to explain concepts to others. Be prepared for questions like this one by practicing a few possibilities ahead of time. This question is asking about your familiarity with injection molding, specifically what types of issues you might see in the parts produced by this process. Injection molding involves molten plastic that is pressurized and injected into a metal tool with a cavity in the shape of the desired part geometry. As the plastic flows through the mold, it will flow faster in some areas and slower in others. These can lead to defects such as drag, flash, and knit lines. This can be avoided by adjusting the wall thickness of the tool or by utilizing post-processing methods such as trimming the excess plastic that occurs at the separation lines (flash).