Near the beginning of the movie, where Jafar is obtaining the scarab, the thief has one half and Jafar has the other. These pieces are made to fit together, and when the thief displays his half before Iago takes it, is has a half-circle cut out of it. When Jafar takes it to put it to the half he already had, the same half now has an additional half-circle-- the piece has changed . . .

(I may have gotten the order wrong, but in any event it does change)