shield animation glitch (wiggle)

I was messing with a new world in creative mode and I equipped a shield on my off-hand, and a golden apple on my main hand. Then I hold right click and the shield wiggles for a split second.

I think it's supposedly a smooth blocking animation.

And it wiggled. (wiggle wiggle wigg, bala ba ba bala, wiggle wiggle wigg)

1. Put a golden apple on the main hand
2. Put a shield on the off-hand
3. Hold/Spam right click to see the wiggle

p.s. sorry for not uploading a video/picture