I was recently reading something in Vayikra (in Chabad.org) and I found a parenthesis in 11:21. I've never seen something like this before.
אַךְ אֶת זֶה תֹּאכְלוּ מִכֹּל שֶׁרֶץ הָעוֹף הַהֹלֵךְ עַל אַרְבַּע אֲשֶׁר לוֹ (כתיב אשׁר לא) כְרָעַיִם מִמַּעַל לְרַגְלָיו לְנַתֵּר בָּהֵן עַל הָאָרֶץ:
It seems that in the Torah it is written אשׁר לא when it should actually be אֲשֶׁר לוֹ . I also checked this in this other website, and it also seems like there was a grammatical error.
Of course it's not an error, but why is it written like this? I haven't found an explanation for this.