English: It was taught in the academy of Rabbi Yishmael: The renewal of Rosh Chodesh was difficult for Moshe until the Holy One, blessed be He, showed it to him with a finger, as it is said, “this month.”
On the daf / in context: See the cited source for the full section.
Type of Learning
Derash on the verse (Mekhilta) — not a formal named middah of the 13.
What Is Learned
Hashem showed Moshe the form of the new moon with a finger because the matter was hard to grasp from words alone.