Mitasek and Slaughtering a Korban
We speak of Mitassek when the person is not aware that he is performing a Mitzvah.”
However, it is reported in the tractate zevahim (47a) that if a person makes the shechita of a korban chatat thinking that it was a chulin animal, then it is invalid. The gemara reports 2 verses to prove this law. But if really we only talk about Mitassek when the person is not aware that he is performing a mitzvah so why did the gemara need to ask for verses? If he thinks this animal is houlin then he is surely unaware that he is fulfilling the mitzvah of slaughtering a korban. The gemara implies that without the verses it would not be considered mitasssek, why?