Witness Reverend Jeff Hood told reporters he saw a man ‘struggling for their life’ for 22 minutes as Smith became the first US death row inmate executed by nitrogen asphyxia
“Kenny just began to gasp for air repeatedly and the execution took about 25 minutes total.”
Firing squad, I'd imagine even though they always used to have 1 shooter with a blank. Hanging, if they had the rope too long it can cause decapitation.