Baba Kama 65a - Stealing with your chatzer

The gemara says that we need the pasuk of "אם המצא" to teach that one need not steal with his hands to be chayev keifel, even if he steals with his chatzer he would also be chayev keifel. The Ketzos HaChoshen (348:2) quotes rashi in Baba Metziah 10b that the case of stealing with one's chatzer is that the animal enters his chatzer and he locks the door on it. Why does rashi not say the simplest case, where the animal enters his chatzer and he has machshava to acquire the animal through a kinyan chatzer. The Ketzos points out that Rashi seems to hold that a thought alone does not qualify as "stealing", therefore he must do an action of closing the door on the animal. Although for acquiring a lost object with a chatzeir, all that it takes is machshava alone, but gezeila cannot be done with machshava, it requires an action. Tosafos also seems to hold like rashi that machshava alone is insufficient. Tosafos (d.h. ein) says that the case is where he hits the animal with a stick forcing it to leave the chatzeir of the ba'al habayis and enter the chatzeir of the ganev. However, Tosafos doesn't simply say like rashi that the animal enters the chatzeir of the ganev on his own and all the ganev does is close the door on it. Tosafos implies that it is necessary to do an act of forcing the animal out of reshus chaveiro and into the reshus of the ganev, such as hitting it with a stick. Tosafos seems to understand that if the animal would enter the chatzeir of the ganev on his own, he would not be considered a ganev by simply locking the gate with the animal inside with the intent of stealing it. Based on this, Tosafos cannot explain that the chiddush of chatzeir is simply that one need not do an action with his hands to be considered a ganev, because Tosafos holds that even stealing with one's chatzeir requires an action b'yadayim. Therefore Tosafos is compelled to say that the chiddush of chatzeir is that it can acquire even when the acquisition itself is an issur such as this case where he is stealing.