1)
Why does he mention Goyim sinking?
1.
Rashi: This is the praise that I will tell!
2.
Radak: Pelishtim fell in the net that they hid to trap us.
3.
Malbim: He explains how the salvation was via Hashgachah, and not chance. They sunk in the pit that they made, and were caught in the net that they hid to trap us.
2)
What is the meaning of "b'Reshes Zu Tamanu"?
1.
Radak #1: It means b'Reshes Asher Tamanu. Also "Zu Chatanu Lo" (Yeshayah 42:24, is like Asher Chatanu Lo).
2.
Radak #2: They hid this net.
