I need help understanding Electric Boomerang

The wiki says: "Additionally, after the initial strike, each boomerang deals 42% (+42% per stack) damage rapidly with a proc coefficient of 0.2."

But there isn't any further information.

My understanding is that it behaves like Sawmerang. Where it gets launched, and returns. So I'm having a difficult time understanding how it could deal damage per second.

For how many seconds? How many times does it hit per second? When does it deal damage per second?