Rashi on Leviticus 5:2/רש"י על ויקרא ה׳:ב׳

1'או נפש אשר תגע וגו‎‎ OR IF A SOUL TOUCH [ANY UNCLEAN THING] etc., and after acquiring this uncleanness eats holy things or enters the Sanctuary, this being something which if done willfully is subject to the penalty of excision — thus is it explained in Treatise Shevuot 14b.

2עלם ממנו‎ונ AND IT WAS HIDDEN FROM HIM — the uncleanness was hidden from him (escaped his notice, not the fact that the things he ate were holy or that the place he entered was the Sanctuary. The translation therefore is “and it — the fact that he was unclean — escaped his notice, but he actually was unclean”) (Sifra, Vayikra Dibbura d'Chovah, Chapter 13 7; cf. Shevuot 14b).

3‎ם‎‎‏ואש AND HE INCUR GUILT through eating sacred food or entering the Sanctuary.