When a football player clocks an opponent on the field, it often does not look so bad—until we see it in slow motion. Suddenly, a clean, fair tackle becomes a dirty play, premeditated to maim (as any bar full of indignant fans will loudly confirm). But why? A study published last August in the Proceedings of the National Academy of Sciences USA suggests that slow motion leads us to believe that the people involved were acting with greater intent.

Researchers designed experiments based on a place where slow-motion video comes up a lot: the courtroom. They asked subjects to imagine themselves as jurors and watch a video of a convenience store robbery and shooting, either in slow motion or in real time. Those who watched the slow-motion video reported thinking the robber had more time to act and was acting with greater intent. The effect persisted even when the researchers displayed a timer on the screen to emphasize exactly how much time was passing, and it was reduced yet still present when subjects watched a combination of real-time and slow-motion videos of the crime (as they might in an actual courtroom). Participants also ascribed greater intent to a football player ramming an opponent when they viewed the play in slow motion.

Werner Helsen, a kinesiologist at the University of Leuven in Belgium, who was not involved in the study, says the findings are in line with his own research on perception and decision making in crime scene interventions and violent soccer plays.

One possible explanation for this slo-mo effect stems from our sense of time, which author Benjamin Converse, a psychologist at the University of Virginia, describes as “quite malleable.” He explains that when we watch footage in slow motion, we cannot help but assume that because we as viewers have more time to think through the events as they unfold, the same holds true for the people in the video.

Converse adds that we often accept video as the absolute truth, even when it has been manipulated. “There are a million things that go into how the video is recorded in the first place and an equal number of variables that go into playback,” he says.

Currently there are no consistent guidelines about using slow-motion video in legal settings, yet whether or not an action is deemed intentional can have a considerable impact on the severity of a suspect's sentence. “We're rapidly reaching a stage in which almost every trial that has a question about somebody's actions is going to be accompanied by a video of some sort,” says study co-author Zachary Burns, a psychologist at the University of San Francisco. “But I think we do need to understand what the limitations are.”