1)
What is "Miftan"?
1.
Rashi: It is a (Radak - the lower) threshold.
2)
Why does it say "El ha'Miftan"?
1.
Radak: This is like Al ha'Miftan, just like "va'Yach Es ha'Pelishti El Mitzcho" (17:49) is like Al Mitzcho.
3)
What is the meaning of "Rak Dagon"?
1.
Radak: It is the [bottom] part with the form of a fish. Refer to 3:2:2:2.
4)
Why were the head and hands distanced from the body?
1.
Malbim: This is lest they think that it fought with the Aron, and the Aron cut off its head and hands, like victors are wont to do. Rather, it was severed by itself, and then bowed and fell in front of the Aron.