1)
Why does it say "Doresh Damim Osam Zachar"?
1.
Rashi: He remembers blood of Yisrael that was spilled.
2.
Radak: He demands retribution for the blood of Aniyim from those who oppressed them, and remembers the blood of Yisrael that Pelishtim spilled.
3.
Malbim: He remembers the nations only for retribution of the blood spilled. However, He does not forget the cries of the humble at all. He does not wait for their blood to remind him; He saves them immediately - "Lo Azavta Dorshecha Hashem" (verse 11).
2)
Why is "Anavim" written with a Yud?
1.
Radak: It is written like Aniyim; the humble are usually poor and weak. The blood reminds him to do Mishpat for the killing.