Aatrox- sated devourer

So I was playing aatrox jungle today, testing him with the improved jungle item Skirmishers sabre - sated devourer I noticed how his W isn't always displayed or animated when he has empowered attack, it just looks like a normal attack (animation, no buff) but it still heals him or deals increased damage. This only happens when his blood well is filled and has high attack speed ( I had these items: Skirmishers sabre , Blade of the ruined king , and berserker's greaves and around 2.30 attack speed) . Thank you for reading.