In William Shakespeare's tragedy Othello, what are two examples (each) of symbolism, foreshadowing, and irony? Please provide full citations.

Symbolism, foreshadowing, and irony are three important
techniques used by William Shakespeare in his great tragedy
Othello.  In fact, one needn’t read very far into the play to
discover at least two examples of each
technique.

Symbolism, for
example, appears when Iago tells Brabantio that Othello and Desdemona are “making the
beast with two backs” (1.1.113).  Rather than simply stating plainly that Othello and
Desdemona are having sex, Iago uses vivid imagery and symbolism to suggest that Othello
and Desdemona are behaving monstrously and unnaturally (at least from the perspective of
Iago and Brabantio).  They are, he suggests, acting like irrational beasts rather than
like rational human beings – a claim that is ironic since
no one will behave in a more monstrous way in this play than will Iago himself.  Further
symbolism can be seen when Brabantio calls
out,

Give me a
taper . . .

Light, I say, light!
(1.1.138,141)

Brabantio seeks
literal light, but he also seeks symbolic enlightenment concerning the truth of the
charges against Othello and his daughter. Ironically, the
enlightenment he receives will darken his life and actually lead to his early death. 
The “light” he seeks here is part of a larger pattern of symbolism of light vs. darkness
that runs throughout the play.  (Later, Othello will both literally and symbolically
“put out the light” when he kills Desdemona
[5.1.7]).

Foreshadowing also
appears very early in the play, as when Brabantio, having discovered that Desdemona and
Othello are indeed married, feels betrayed and warns
Othello,

Look
to her, Moor, if thou hast eyes to see:

She has deceived
her father, and may thee.
(1.3.287-88)

This warning, of
course, foreshadows Othello’s later murderous suspicion that Desdemona has indeed been
unfaithful to him. Ironically, however, Othello does not
really use his “eyes to see” Desdomona as she truly is (loyal and faithful) but rather
is deceived by Iago, not by Desdemona.  Further ironic
foreshadowing appears when Iago tells Roderigo that human
beings “have reason to cool our raging motions” (1.3.325) – a statement that foreshadows
Othello’s “raging motions” as well as his later failure to use his
reason.

Meanwhile, much of what Iago says throughout the
play exhibits irony, as in the words just quoted.  Iago
himself is full of “raging motions” (particularly in his vindictiveness toward Othello),
so it is ironic that he should counsel anyone else about giving in to passion. 
Moreover, Iago uses “reason” only in the most debased and corrupted senses of the word. 
Instead of using reason to “cool” rage, Iago uses reason to promote rage in himself and
others, whom he thereby manipulates.  This is why the term “Honest Iago” (1.3.289) –
which is used repeatedly throughout the play – is one of the most ironic terms in all of
Shakespeare.