What is the meaning of "Hispalshi"?
Rashi: Roll [in the ashes].
Radak citing Targum Yonasan: Cover yourself and dwell [in the ashes].
What is "Evel Yechidi"?
Rashi: It is mourning over a lone child - one who had only one son, and he died. Radak - this is a harsh mourning.
Malbim: Everyone should mourn alone; do not mourn together.
Why is there a Patach under the Pei in "Mispad"?
Rashi: This is because it is Samuch to "Tamrurim" (bitterness).
Why does it say "Ki Pis'om"?
Radak: Begin eulogizing now, for you do not know when the enemy will come; it will be sudden.
Malbim: The enemy will come at this moment.
Why does it say "Aleinu"?
Rashi: It is as if the enemy comes against Me and you.