D3 xp bar sparks

Hey we were playing multi player on my brother in laws xbox and his exp bar had little sparks at the right end. Can anyone explain what this is please?

If it is not a Pool of Reflection or some other effect that might grant additional XP, such as a Ruby in the helm, multiple different items, etc., then it could be a graphic artifact from a skill coming off cooldown or something, where the circle that indicates it has completed got “lost” and is still spinning, causing what might be a “sparkle.”

But, this is guessing without seeing.