Olenna Tyrell: Will there be pain? (meaning after taking the poison Jaime’s given her)
Jaime Lannister: No. I made sure of that.
Olenna Tyrell: That’s good. I’d hate to die like your son. Clawing at my neck, foam and bile spilling from my mouth, eyes bloodred, skin purple. Must have been horrible for you, as a Kingsguard, as a father. It was horrible enough for me. A shocking scene. Not at all what I intended. You see, I had never seen the poison work before. Tell Cersei. I want her to know it was me.
From Game of Thrones – Season 7 Episode 3: ‘The Queen’s Justice’ (7×03)