Consider the scenario below. As an optional discussion, respond with a substantive response.

A researcher evaluated the effects of video game content on mood. One group was randomly assigned to play a 30-minute videogame in which there was no violence and rewards were achieved by virtually cooperating with other players. The other group was randomly assigned to play a 30-minute video game in which there was violence and rewards were achieved through virtually competing with and/or hurting other players. At the end of the 30 minutes, all players completed the same questionnaire, in which they rated their mood on several dimensions (e.g., happiness, boredom, anger, frustration). Is there a possible flaw in this design that might make it difficult to interpret the results or threaten the study's validity? If yes, why? If not, why not? Be specific.