If one slaughtered with the smooth edge of a hand sickle, with a flint or with a reed, the slaughtering is valid. All may slaughter; at all times one may slaughter; with any implement one may slaughter, excepting a scythe, a saw, teeth or a fingernail, since these strangle.
The Gemara points out that the expression used by the Mishnah, that slaughtering with the abovementioned implements is valid, indicates that the shehitah is valid ex post-facto, but that ideally it should not be used. In the case of a hand sickle, or magel yad, the Gemara suggests that the reason for this is obvious – we fear lest the slaughterer might use the wrong side of the sickle, which would be invalid. According to Rashi, the wrong side of the magel yad has a serrated edge, while according to the Ra’avad, the magel yad is a type of axe, and the wrong side is sharp, but pointed and not long enough to perform shehitah.
Regarding the flint (tzur) and the reed (kaneh), the Gemara explains that if they were properly sharpened and were not connected to the ground they can be used without any concern. If they were still connected to the ground, they cannot be used at all. The Mishnah’s case, where using them is acceptable after-the-fact, is where they were removed from the ground but afterwards were reconnected.
The implements in the Mishnah that are invalid for slaughter include a scythe (magel katzir), a saw, and teeth, which are problematic because they are not smooth and their irregular edges tear at the animal’s windpipe and esophagus that must be cut smoothly. The Gemara explains that the problem with using a fingernail for slaughter is a different one; it is considered “connected” which, as we learned, is invalid, even though in this case it is not connected to the ground, but to the slaughterer’s body.