What is the meaning of "Tzevis Leyatzava"?
Rashi: I wanted to understand the Emes [the fourth Chayah]. Malbim - Tzevis is desire; Yatzava refers to Emes.
What did he want to know about the fourth Chayah?
Malbim: Since Ketz ha'Yamin will be after the fourth Chayah (kingdom) ceases, he wanted to know (a) Why it was different and scarier than the others. It had iron teeth and copper claws (which were not mentioned before). In Nebuchadnetzar's vision of the image, he saw toes of iron mixed with Cheres. This refers to the kingdoms that will be at the end (the 10 horns). He already saw them when the fourth Chayah stood. Immediately it seized kingship over all 10 kingdoms into which it will split at the end 1 .
Malbim (20): He also wanted to know about the 10 horns, and the horn that sprouted and three that fell due to it.
How was it different than the others?
Rashi: It was exceedingly scary.
