Rav Meir pointed out the difficulty in understanding the connection between the scissors and ochel nefesh. He explained that since it is used for getting money for ochel nefesh, therefore it is related. Rabbeinu Tam does not like Rashi's explanation and is goreis "zug shel misparayim" -- scissors used for cutting vegetables (we saw this earlier, no?). Additional explanations brought by the Rosh are scissors used to cut the beis hashechita.
What about tzemed shel Paros, which has the same problem? Rosh there says שדרכם לרכס בתבואה. In case you forgot what this is referring to (I did) , see gemara 89b that discusses פרות המרכסות בתבואה, a part of the process of preparing barley for food where the cows are used to remove the the shells.