This entire branch of the discussion is being buried in downvotes, but that is actually a very good analogy. Except in the case of Alexa, it's like you are holding the onion and someone else is slicing it. With a very sharp knife.

Analogously, the purpose of an Echo is to listen.

A sheath is an off-switch for a blade.

Don't think this analogy really applies. I mean you have complete control of the knife - it's a physical tool you hold in your hand. Can't compare this with any electronic device at all, which always does lots of stuff behind your back.

But as the owner of the Echo, which only transmits after the wake word, you are the one that wields that knife.