The bug

When the player is damaged or heals, the hearts displayed above the hotbar will blink accordingly. The same does not happen for horses and other rideable mobs, despite the existence of dedicated textures for this purpose. These textures are present in icons.png as of 1.20.1, but remain unused (MC-237326, MC-237427).

How to reproduce

1. Take damage yourself
2. Have a mob you're riding take damage
3. Compare visuals

Expected results

Flashing in both cases.

Actual results

It only happens for the player - the rideable mob's decrease with no extra visual indication.

How to fix

I've attached the three textures needed for this to work, extracted from a 1.20.1 icons.png file. These textures are to be placed in assets/minecraft/textures/gui/sprites/hud/heart. Code changes will be required for the game to actually use these textures.