Trying to make this animation look smoother

 img {
          width: 10rem;
          filter: grayscale(1) invert(1);
          overflow: clip;
          animation: upanddown 1s infinite;

          @keyframes upanddown {
            0% {
              transform: rotateZ(-6deg);
            }
            25% {
              transform: rotateZ(-3deg);
            }
            50% {
              transform: rotateZ(0deg);
            }
            75% {
              transform: rotateZ(3deg);
            }

            100% {
              transform: rotateZ(6deg);
            }
          }
        }