Brief Description: 
Placing a block next to a mob sometimes doesn't display the hand animation.

Steps to Reproduce:

1. Spawn a mob. (I'd recommend spawning a horse as these move quite slow and will make reproducing this bug much easier).
2. Wait until it begins moving.
3. Stand behind it and keep clicking on the area you want to place the block.
4. When you click at the right time, it won't display the hand animation. (See video below).

Observed Results:
It doesn't play the hand animation

Expected Results:

It should play the hand animation

Screenshots/Videos:

I've attached a video which shows this bug in action. I simply waited for the horse to move forward and kept clicking where I wanted to place a block. Once the horse moved out of the way, if you time it right, you can place a bock without it displaying the hand animation.

Notes:
I believe that this works with any mob that walks along the ground.