Makhshirin, Chapter Three, Mishnah Six
1) If his olives were put on the roof and rain came down upon them and he was glad of it, it comes under the law of if water be put.
2) Rabbi Judah said: one cannot help being glad of it.
a) Rather, [it comes under the law] only if he plugged up the gutter or if he shook the water [onto the olives].
Section one: According to the first opinion the olives are susceptible to impurity as long as the person is happy that the rainwater came upon them. If he wanted them to stay dry, they are not susceptible. Again, his inner thoughts are what determine the susceptibility of the produce.
Section two: As he did in yesterday’s mishnah, Rabbi Judah says that a person will always be happy when rainwater comes upon his olives. Therefore, in order for them to be susceptible he must physically do something to get the rainwater on them. There are two possibilities. Either he stops up the gutter so that the roof fills up with water, or he shakes water onto the olives.