In Shakespeare's Macbeth, some of the unnatural behaviors that make Lady Macbeth seem "witch-like" include her summoning of the spirits of darkness to help her carry out her part in murder, her professed willingness to kill a child if necessary, and her ability to smear the guards with the king's blood after Duncan is dead.
In Act One, scene five, Lady Macbeth she calls on the spirits of darkness to help her become less like a woman (nurturing and caring) so that she can take part in Macbeth murder of the King.
Come, you spirits
That tend on mortal thoughts... (41-42)
She asks them spirits to make her less like a woman, which is unnatural:
...unsex me here;
And fill me, from the crown to the top, top-full
Of direst cruelty! (42-44)
In Act One, scene seven, Lady Macbeth says that she knows what it is like to have a child and nurse it, but if she had promised Macbeth to kill the child, she would not hesitate—as it looked trustingly in her face:
I have given suck, and know
How tender ’tis to love the babe that milks me:
I would, while it was smiling in my face,
Have pluck'd my nipple from his boneless gums,
And dash'd the brains out... (61-64)
This is not normal.
After Macbeth has killed Duncan, Lady Macbeth has to return the daggers her husband used (that would implicate them in the murder) to the King's chambers because Macbeth is unable to do so. She acts like she does it every day.
Why did you bring these daggers from the place?
They must lie there. Go carry them, and smear
The sleepy grooms with blood.
I'll go no more:
I am afraid to think what I have done;
Look on't again I dare not.
Infirm of purpose!
Give me the daggers...
If he do bleed,
I'll gild the faces of the grooms withal,
For it must seem their guilt. (II.ii.61-62, 64-72)
There she rubs the blood of the King on the drugged guards so that it will seem as if they have committed the murder. It is Lady Macbeth's intent that no one will suspect her and her husband of duplicity in Duncan's murder. The ease with which she conducts herself in this is also aberrant.
When Lady Macbeth returns, she condemns Macbeth, noting that her hands are now covered with blood, but that she would be embarrassed to be as fearful as he is. This, too, is unnatural: first, what woman would be able to carry out this task, but also what woman would have the kind of ease with the situation to insist that being fearful would embarrass her?
My hands are of your color, but I shame
To wear a heart so white. (80-81)
The witches deal with death. In Act Four, scene one, they concoct a spell, calling on evil spirits to assist them. Their potions have body parts, including the liver of a blasphemer, and...
...poison'd entrails… (5)
Nose of Turk and Tartar's lips,
Finger of birth-strangled babe... (29-30)
Then Hecate tells them to dance, and they sing...to "Black spirits."
The witches' job on earth is to win souls to their eternal damnation. In a Christian society (as Elizabethan England was), this behavior would seem believable (for they were certain there were witches), but unnatural and evil.
Lady Macbeth mimics their evil behavior in calling on evil spirits, "practicing" in death, and even using the blood of the dead King to her purpose. She may not look like a witch, but her behavior is "witch-like" and unnatural.