"smear
The sleepy grooms with the blood."

But Macbeth's nerve is gone; he is physically broken now as well as
mentally o'erwrought; he cries:

"I'll go no more;
I am afraid to think what I have done.
Look on't again I dare not."

All this is exquisitely characteristic of the nervous student who has
been screwed up to a feat beyond his strength, "a terrible feat," and
who has broken down over it, but the words are altogether absurd in the
mouth of an ambitious, half-barbarous chieftain.

His wife chides him as fanciful, childish--"infirm of purpose,"--she'll
put the daggers back herself; but nothing can hearten Macbeth; every
household noise sets his heart thumping:

"Whence is that knocking?
How is't with me when every noise appals me?"

His mind rocks; he even imagines he is being tortured:

"What hands are here? Ha!
They pluck out my eyes."

And then he swings into another incomparable lyric:

"Will all great Neptune's ocean wash this blood