My own eyes to bear on her so that I thought
Could I keep them one half-minute fixed, she would fall
Shrivelled; she fell not: yet this does it all!
X
Not that I bid you spare her the pain;
Let death be felt and the proof remain:
Brand, burn up, bite into its grace—
He is sure to remember her dying face!
XI
Is it done? Take my mask off! Nay, be not morose;
It kills her, and this prevents seeing it close:
The delicate droplet, my whole fortune's fee!
If it hurts her, beside, can it ever hurt me?
XII
Now, take all my jewels, gorge gold to your fill,
You may kiss me, old man, on my mouth if you will!
The speaker hesitates for only a moment, and that relates to the possibility of the poison affecting herself.  The question relates to the danger to her own life or whether she could be caught.  Either way it is a practical rather than a moral hesitation.
The Laboratory