We cannot know for sure, though, that there is not something else affecting it. An example of a "hidden cause" might be that sugar dissolves faster each time more sugar is dissolved into the same pot. This is probably not true, but if it were, it could make the results exactly the same: three trials, and the last one would be fastest. We have no reason to think that this is true at this time, but we might want to note it as another possible answer.