According to the story described in the book of Exodus, after the people of Israel escaped Egypt, Moses climbed the Mount Sinai, where God gave him two stone tablets with the famous and well-known "ten commandments." These commandments are listed in that part of the story (in Exodus 20.)
Moses spent a long time there, and when he descended from the mountain, he saw that the people of Israel were worshiping a false god, he got extremely angered, broke the stone tablets and ordered the perpetrators to be killed (way to obey the commandment he just got about not killing, but that's besides the point here.)
After the whole mess was sorted out, he climbed the mountain a second time and got two new tablets with the commandments.
This is the version of the story that 99.9% of Christians know and love. But here comes the tiny detail that, quite amazingly, very few Christians are aware of: The commandments written on that second pair of tablets are quite different from the first ones. (A few of them slightly resemble their counterparts in the first set, but the majority are completely different.)
What makes this especially egregious is that the scripture explicitly states that these new tablets contain the same commandments as the previous one. The beginning of the chapter (Exodus 34) that describes God giving Moses the second pair of tablets explicitly and unambiguously states:
The Lord said to Moses, “Chisel out two stone tablets like the first ones, and I will write on them the words that were on the first tablets, which you broke.This is not something that's up to interpretation. It couldn't be much clearer than that. It quite explicitly states that the words are the same as those on the first tablets. Yet quite obviously they are not.
Moreover, and even more egregiously, after the new commandments are listed in this chapter, they being the ten commandments is then explicitly reinforced like this:
Then the Lord said to Moses, “Write down these words, for in accordance with these words I have made a covenant with you and with Israel.” Moses was there with the Lord forty days and forty nights without eating bread or drinking water. And he wrote on the tablets the words of the covenant—the Ten Commandments.
It couldn't get more explicit than that.
This is a well-recognized discrepancy among biblical scholars. The two sets of commandments actually have names: The well-known ones are named "the ethical decalogue" and this new set of commandments is named "the ritual decalogue."
Yet, among most non-scholar Christians, even those who study the Bible a lot, this is surprisingly little-known.