A Researcher Believes That Thinking About Clowns Will Make People

A researcher believes that thinking about clowns will make people more aggressive. He randomly assigns some people to see pictures of clowns, and other people to read a description of a calm forest. He finds that people who looked at pictures of clowns behave more aggressively. However, there is at least one confound in this study. What is that confound?

A) The researcher has no theoretical basis for this effect.
B) Not all people will become aggressive when they think about clowns.
C) Some people looked at pictures, while others just read text.
D) Looking at pictures of clowns may not have been a good operational definition of thinking about clowns.