There are probably many other variables on which the two groups differ. Parental smoking is confounded with the use of candy cigarettes, therefore, the conclusion is not justified. The students that go to each college may differ, not just the courses. There is an order-effect confound. The drug treatment is confounded with the amount of practice.
Litter is confounded with treatment.
Need some pups from each litter to be in each treatment group. Differential attrition in groups means that the subjects in each treatment might not have been equivalent in ability to do task. For example, they ones who went to the Y might be more social. Need to rule out competing hypotheses like fatigue or that the specific test is harder than the others. The experience of the judges is confounded with the method of testing.