27. Since the knife must be checked before (15) and after (16) the shechita, one who shechts many animals or birds must check the knife between each one. If he checked after each one and found a nick in the knife after the final shechita, all besides the last one are kosher.
28. If he did not check between each shechita and saw after the final shechita that the knife had a nick, all of them, including the first, are sofeik neveilos, as the knife might have gotten a nick on the skin of the first animal before shechting its simanim. If that happened, they were all shechted with a posul knife and are neveilos (שו"ע סי"א ).
29. Willing to have a sofeik. If one is willing, he may enter a sofeik by only checking the knife after shechting multiple animals or birds; if the knife is found to be nicked in the end, it will ruin all the shechitos (רמ"א שם ). It is unlikely one would do this for expensive animals, as he might lose a lot of money; it would be better to take the trouble of checking the knife before each animal than to lose the value of multiple animals.
30. When shechting chickens, which are not so expensive, sometimes it is worthwhile to risk shechting many chickens by only checking the knife at the end, thus avoiding having to pause after each chicken to check the knife. In modern shechita houses, the shochet only checks after many chickens; some check every three minutes, some every five minutes or longer. Each shechita house follows the instructions of its rav and its level of kashrus. From a financial perspective, it makes more sense to shecht large quantities of chickens in a short time and check the knife afterward than to take pains to check after each chicken.
31. Number of inspections between shechitos. Although some hold a shochet who checks every couple minutes should do 12 inspections (23), the prevalent minhag is to just do two – back and forth over the sharp edge (25) – and to rely on an inspection while the knife is wet, even though the quality of the inspection is not as good as when the knife is dry.
