A large medical device manufacturer asked us to perform a human factors study on an autoinjector. We observed some inversions where users would have injected their thumbs instead of the desired injection site if the device they were using had been real. The cap and button were both the same color, making it difficult for patients to determine which end had the needle when referring to the Instructions for Use (IFU). While the client knew this was a possibility, it wasn't possible for them to change the cap or button colors.
One of the subjects who inverted explained that the graphic of the device in horizontal orientation in the IFU didn't do enough to show where the needle would come out because the cap and button are the same color. The client came to the solution that they could show the device in a vertical orientation, with the needle pointing down.
When we re-tested after the change to the IFU we did not see any inversions.