Very interesting back story to the feet nailing. I just cannot imagine the pain of having each of your feet nailed separately.
Further to this, yes, it is hard to truly encompass the incredible pain of having big iron spikes driven through each of your wrists and feet, one by one, with each of those nails requiring maybe a dozen blows of a heavy hammer. So it's not just a sudden piercing of your flesh; each blow sends the rough edges of a square nail rasping through muscle, tendon, bone and nerves, and hammering just one of those nails into place might take a minute or so from start to finish.
Before Sabina was a crucifixion victim, she was part of the crowd at many crucifixions, shouting along with the rest because that's what you did when you watched a crucifixion. Here's what she said in recounting the crucifixion of a man:
He continued to plead and became hysterical when Antius pressed the point of a nail against his wrist and raised his hammer. His babbling was cut off with an agonized scream as the first blow of the hammer fell. Verina and I laughed out loud at the ridiculous way his cock flopped from side to side as his body jerked following each blow of the hammer, like the shock of the hammer would travel down his body and come out there. It was so funny to watch!
And later in her prison cell on the day before her crucifixion, Sabina talks with Salonina about nailing. She doesn't really want Salonina to know that she's been going to watch crucifixions and so knows how they go.
“Now Sabina, the executioner will want to drive that first nail quickly. He’ll try to drive it straight through and into the wood with the first blow to pin your wrist to the crosspiece. If he gets it right, his helpers don’t have to hold your left arm any longer. With them out of the way, he’s free to take bigger swings with his hammer.”
“And… if he doesn’t get it right?”
“Then he has to hit it again, but if it’s already halfway through your wrist, and you’re struggling, he’ll have to shorten his swing to be sure he hits it. Every one of those hammer blows hurts.”
“I- I know,” Sabina said. I’ve seen the way they all scream, every time… each time the hammer comes down. How the shock… it makes their whole body jump, like… like you can see the pain like a wave, going right down their body, all the way to their toes!”
Then when her wrists are being nailed, Sabina describes what she is feeling:
The hammer seemed to hang high above me for a long time, then come down in slow motion. My eyes followed its arc until it hit the head of the spike. An instant later I felt the shock and stabbing pain as the point of the nail grated between the bones of my wrist. I heard someone scream and realized that it was coming from my own throat. I was twisting and writhing in agony underneath Ajax, who was on top of me. The hammer came down again and again, driving the spike deeper into the timber, rough iron grating against bone, wedging the bones in my wrist apart, sinews snapping.
And finally, as her feet are being nailed the agony is even worse because the shock of the hammer blows travels through the timber and vibrates the nails in her wounded wrists.
As I had when my wrists were nailed, I felt the shank of the spike grating between the bones of my foot, forcing them apart. The cross trembled with each blow as the executioner continued to hammer the spike deeper into the timber. The shock traveled through the wood and nails, vibrating the iron between the bones inside my wrists, creating a horrible new agony.
I have no way of knowing whether or not a victim would notice that added pain in her wrists but I think it's a possibility.
One other point I'd mention is that in all of man's history up until the late 19th century or so, there was an expectation and acceptance of severe, maybe excruciating pain. Teeth were extracted, broken bones set, wounds cleaned and sewn up, limbs amputated, and surgery performed all without anesthetic. This being the norm, perhaps punishments that were no worse than the norm wouldn't have the same impact on the onlookers and thus would not serve their purpose as a deterrent to criminals.