How does the Enraged monster modifier work on companions?

I've been testing this modifier for hours on end, and I don't quite understand when it triggers.

(I'm aware there are two different Enraged modifiers, Periodicically Enraged, and Enraged. I'm using Enraged, and it's triggered somehow)

I've seen that sometimes when swapping weapons to resummon the companion while in combat, it becomes enraged. During the next 10 ish seconds it goes in and out of enraged when enemies are close and far respectively.

Does anyone here know more? The Wiki doesn't describe anything about it.