When I was testing the warden, I had noticed that the warden was detecting its own exp on death. I don't think I had seen it before but it started to detect the exp on death.

To replicate this behavior, summon a warden with the gamerule domobloot true, then kill a warden and stand back as the exp will send vibrations as they hit the ground to the warden in its death animation.

Also the picture is really hard to get but you can see it is detecting the exp by the glowing on its sensors.