They contacted him and he apparently claimed that he broke the teeth on a shredder with a screwdriver. The teeth on shredders exist only to make "cross cuts". The previous generation of shredders did not have them, and cut the paper into long strips instead of confetti; which is fine for most purposes. So a claim that removing teeth prevents shredding is bogus.
(Edited to add) thinking about it, this could be an honest mistake. You could "remove the teeth with a screwdriver" by disassembling the shredder and removing some blades from the axle, which corresponds to how the shredder in this paper was supposed to work. If Dan Ariely got a grad student to modify the shredder, he could simply have misunderstood their explanation of how they did so. How the shredder was modified was not, after all, important to the experiment.
(Edit 2) Although, those who ran the experiment would need to keep the missing teeth out of the line of sight of the subjects.
(Edited to add) thinking about it, this could be an honest mistake. You could "remove the teeth with a screwdriver" by disassembling the shredder and removing some blades from the axle, which corresponds to how the shredder in this paper was supposed to work. If Dan Ariely got a grad student to modify the shredder, he could simply have misunderstood their explanation of how they did so. How the shredder was modified was not, after all, important to the experiment.
(Edit 2) Although, those who ran the experiment would need to keep the missing teeth out of the line of sight of the subjects.