What was their lust for their Pilagshim?
Rashi: They lusted to be Pilagshim to them (Egypt).
Radak citing the Meforshim: Pilagshim are their slaves. Here, it is men, and not women. It says "Asher Besar Chamorim Besaram", i.e. their male organ, like "Rar Besaro Es Zovo Oh Hechtim Besaro mi'Zovo" (Vayikra 15:3).
Radak: "Al" is like Im (their lust was with their Pilagshim), like "va'Yavo'u ha'Anashim Al ha'Nashim" (Shemos 35:22). [Yehudah] desired them to the point that they seemed to them like their Pilagshim, and not their wives. The Targum is like this ? they desired to be Shemota 1 to them. Some texts of the Targum say Shamsha, like a Shifchah.
Malbim: They lusted to the point that they were together with their Pilagshim. They were to [the Egyptians] like a Pilegesh designated for Zenus and to be a Shifchah.
I.e. the Egyptians would slip away from their wives in order to be with them. (PF)
Is their flesh like that of donkeys?!
Rashi: Their male organ is like that of donkeys.
Radak #1: This refers to the Pilagshim. Also a female's Ervah is called Basar ? "Dam Yihyeh Zovah bi'Vsarah" (Vayikra 15:19).
Radak #2: This refers to Egyptians and Kasdim. Their Ervah is compared to donkeys, which grow flesh [of the Ever]. This is said for disgrace ? the Egyptians' deeds are repulsive, and even so [Yehudah] desired them and learned their lowly deeds! This is the Mashal of their Pilagshim. Even though it mentioned Zenus Mitzrayim at the beginning (3), it mentions it also [here] at the end, for it was her first Zenus and the reason for their Zenus all the time that they were Mezanah.
Malbim: They need many Pilagshim (to fulfill their great desire for Bi'ah, like donkeys). They were submissive to Egypt, with the other nations subjugated to them. They are called Somechei Mitzrayim, i.e. Kush, Put and Lud.
What is "Zirmas"?
Rashi: It is an expression of great Bi'ah. Male horses have Bi'ah more than males of any other species of animal. Zirmas is the flow of semen, like "Zerem Mayim Avar" (Chabakuk 3:10).
