וַיִּמְלְא֥וּ יָמֶ֖יהָ לָלֶ֑דֶת וְהִנֵּ֥ה תוֹמִ֖ם בְּבִטְנָֽהּ׃
When her time to give birth was at hand, there were twins in her womb.
Genesis 25:24 (The Contemporary Torah, JPS 2006)
There's a spelling "corruption" in Genesis 25 in the word "twin."
The normal way to spell it is תְּאוֹמִים, te'omin. But in Genesis 25:24, it's spelled תוֹמִ֖ם, tomin.
The rabbis say this "corruption" teaches us that only one twin will be righteous.