Again, the sample size is rather small. Animals are less susceptible to the placebo effect than humans, but the experimenters sensibly included a normal potato placebo. Double blind is not mentioned, but we can assume it is used. The real problem here are the numbers: rats fed non-GM potatoes sprinkled with the toxin still lost 55% of their body mass. These are very ill rats. Trying to determine whether the extra 5% for the GM potatoes was due to supplying the toxin via GM or due to other variables (such as random chance, especially in such a small sample) is difficult to say the least.