What is the meaning of this rebus?

marcus Brutus
john wilkes Booth
Billy the kid
Bonnie parker
clyde Barrow

Letter Equations are well known phrases or facts where the key words have been replaced with the first letter of that word. These are often in the form of an equation, which contain a number, an = sign and the rest of the obscured phrase or fact.

3 = S in the F V of C C (N, P, S M)

Change COLD to HEAT by changing one letter at a time. Each change must produce a valid word in the English language. But there is a catch. You must make the change by going through COOL and WARM. No word can be used more than once.

COLD ---- COOL ---- WARM ---- HEAT

Each of the following sentences contains clues to a set of three words that are spelled the same, except for one letter (each sentence describes a different set). Example: malt, melt, molt.

1) The subject of the meeting was "The Poisonous Elixir".

2) When the man refused to fight, it caused the bully to shout "Are you chicken?".

3) When the cows heard the snake shake, there was a fight for survival.

4) Unable to see, the doctor was still ...