The Gemara's conclusion is that if a שור פקח falls into your bor during the day, then you are patur. However, the Rambam rules in 12:16 in Nizkei Mammon that if the shor only got damaged then the owner of the Bor would be Chayav.
The Raavad asks the obvious question -- if the shor is פקח then what is the basis to differentiate between damage and death? You should be completely patur for this שור פקח. Interestingly, The Raavad is ok with the Rambam stating that for a person who gets HURT, that you would be chayav even though for the animal you should not.
Explaining the Raavad is simple, since we have learned about people אין דרכן של בני אדם להתבונן בדרכים so this leads to a chiyuv for a person that falls into the Bor while still being patur for a שור פקח . The Maggid Mishne explains that perhaps since a person thinks so he does not look around as carefully as a Shor.
So, now we just need to understand the Rambam.
The Maggid Mishne explains that this פקחות of the animal only means that it avoids a serious pit that could kill it but its not smart enough to avoid all damaging obstacles. Based on this, the question arises -- what if the animal falls into a bor that COULD have killed it but only got hurt. Using this logic, do we say that the בעל הבור is patur? The Aruch Hashulchan (choshe mishpat 410:24) says yes. Minchas Chinuch also thinks that this would be correct but says there is no indication of this in the Rambam so he writes ויש ליישב