Lady Macbeth tells her husband to "look like the innocent flower/ But be the serpent under it." Explain what she means.

Essentially, this line is Lady 's warning
to
her husband in how to engage in immorality to get what they both want. 
She says this to him in
, sc. 5, when he tells her thatis coming. 
Ladyrecognizes this as the perfect opportunity for
Macbeth to kill Duncan and
seize power.   In order to become King,realizes that Macbeth must
kill
Duncan.  She also understands that he lacks the vocabulary and full understanding to
do
so.  As a warrior and a fighter on the battlefield, murder is done in name
of King and country
and there is little duplicity involved.  The slaughter is
understood.  Lady Macbeth shrewdly
realizes that her husband might need some
level of guidance in how to murder for personal gain. 
It is in this where
she advises him to "beguile time," and put on pretenses as if he
is a
gracious host, and devoid of any malicious intent.  The "serpent under it" is
how
she believes Macbeth will best understand what needs to be done in how
the murder should be
executed.  In this line, Lady Macbeth's initial
deviousness is evident, something that will
change over the course of the
play.  At the same time, Macbeth's overall innocence is also
evident,
something that will also change over the course of the play.