The Bug:

Mounting entities while holding spawn eggs doesn't play the hand animation.

Please note that if you were to mount some select entities while holding that said entity's spawn egg, a baby would be summoned so in order to reproduce this issue, use any spawn egg that isn't the same as the said summoned entity.

Steps to Reproduce:

1. Summon a pig, saddle it, and obtain a fox spawn egg.
2. Mount the pig while holding the fox spawn egg and watch your hand closely as you do this.
3. Take note as to whether or not mounting entities while holding spawn eggs plays the hand animation.

Observed Behavior:

The hand animation doesn't play.

Expected Behavior:

The hand animation would play.