The verse
Around 1000 BC, David wrote the psalm Jesus quoted from the cross. Halfway through, the man in the psalm is surrounded:
"For many dogs have encompassed me; the council of the malignant hath besieged me. They have dug my hands and feet."
Psalm 21:17 (22:16 in most Bibles)
Hands and feet, dug through. That is what nails do.
Like a lion
Open most printed Hebrew Bibles today, and that verse reads differently. The key word is ka'ari, which means "like a lion."
That leaves the sentence as: the council of the malignant has besieged me, like a lion my hands and my feet. There's no verb. Nothing happens to the hands and feet at all.
They dug
Long before Jesus was born, Jewish scholars translated the Hebrew Bible into Greek. That translation, the Septuagint, was made in the centuries before Christ. At this verse, it reads:
"ōryxan cheiras mou kai podas." They dug my hands and my feet.
The Greek translators were reading a Hebrew copy older than any we had. And they read a verb.
One letter
Here is the difference, written in Hebrew:
Yod is a small hook. Vav is the same hook with a longer stroke down. Written by hand, in ink, on animal skin, the two are easy to confuse.
The scroll
Then the caves by the Dead Sea gave up their scrolls. From a cave at Nahal Hever came a fragment of the Psalms, copied around AD 50 to 68. It is the oldest surviving copy of this verse in Hebrew.
It reads ka'aru. They dug.
The oldest Hebrew copy and the oldest translation agree. David wrote that they would dig through his hands and feet.
What happened
Thomas wouldn't believe until he saw "in his hands the print of the nails." Jesus answered, "Put in thy finger hither, and see my hands" (John 20:25 and 27). To the others he said, "See my hands and my feet, that it is I myself" (Luke 24:39).
Two verses later in the same psalm comes, "They parted my garments amongst them; and upon my vesture they cast lots" (Psalm 21:19). At the cross, the soldiers did exactly that (Matthew 27:35).
Why this is a big deal
The most direct prophecy of the nails in the whole Bible hangs on one letter. And the oldest witnesses we have, a Greek translation from before Christ and a Hebrew scroll from the first century, both read it the same way Christians always have.
A thousand years before the cross, David wrote that they would dig through the Messiah's hands and feet. The oldest copy says so.