What is the purpose of intimidating the witnesses?

Iyun Yaakov: Even though any money wrongfully awarded can be recovered, the false witnesses would still have violated a prohibition. Therefore, we intimidate them to prevent them from transgressing.

How is the lack of rain despite the rainclouds a suitable punishment for false testimony?

Tapuchei Zahav: This is a form of 'measure for measure'. A false witness creates the illusion of truth - something that appears real but is ultimately a lie. Likewise, dark clouds suggest rain is coming, but none falls. The sky "testifies" falsely, just as the witness did.

Why does Rava's Pasuk in Mishlei mention three things - a club, a sword and a sharp arrow?

Vilna Gaon on Mishlei: These three weapons represent varying degrees of punishment for false speech, reflecting the severity of the lie. The club (Meifetz), is the harshest, capable of smashing stone, symbolizing the most severe form of death. The sword is less severe, and the arrow represents the lightest form of punishment. The Gemara in Shevuos 31a discusses three cases of false testimony. The most serious is when someone testifies falsely to extract money, deserving the harshest punishment - the club. A less severe case is when a student, relying on his Rav's assurance of honesty, testifies to something he did not witness. Though well-intentioned, it is still false testimony and punished by the sword. The lightest case is when one witness has already testified, and a second person falsely joins him to complete the pair. This too is falsehood and is punished, though more lightly - symbolized by the arrow.

What is unique about one who incites to idolatry that we do not argue in his defense?

Iyun Yaakov: For all other sins, Beis Din argues on behalf of the accused, as he may not be knowledgeable or sharp enough to defend himself. But one who incites others to idolatry is, by his very nature, crafty and calculated, and certainly capable of defending himself. Therefore, the court does not argue in his defense.

Since Chava was the one that added to Hash-m's command by saying that they were forbidden from touching it, why was she convinced afterwards that therefore one could also eat it and not die?

Toras Chaim: The original command not to eat was in fact only given to Adam. It was Adam who added that Hash-m had also commanded not to touch it.

How does Rav Meharshiya bring proof from the Pasuk of "Its length shall be two and a half Amos"?

Rashi: The word for 'two Amos' is written אמתים. If one would remove just one letter - the Alef, it would spell out the word 200. It is one letter added to the word that reduces it from 200 to 2.

Maharsha, Vilna Gaon (Kol Eliyahu 73), Toras Chaim, Rashash: The phrase 'and a half' is spelled 'וחצי'. If one would remove the letter Vav, the entire phrase would mean 'two Amos are half its length', so that its full length is four Amos. So the extra letter Vav reduced its size from four to 2.5 Amos.

And what is Rav Ashi's proof?

Yad Ramah: The words for twelve are שתי עשרה. In the Pasuk, the phrase used is עשתי עשרה which means eleven. So just one extra letter ('Ayin') reduces it from twelve to eleven.