MentalEdge

I'm not sure on the answer myself, but you did get one thing wrong.

Even the oldest, sickest pet will still make an effort to keep themselves alive however they can: eating, drinking water, moving out of the way of danger, etc.

No, they won't.

Plenty of illnesses cause apathy, dehydration, or loss of appetite.

Causes vary from pain so intense moving is unbearable, or nausea so severe food is inedible. It can be mental, physical, easily treated, or incurable and eventually lethal.

Either way, pets can and absolutely do choose inaction when miserable enough.

!moomin@sopuli.xyz

Let's do crime!

Well, you can apparently also use supercritical carbon dioxide.

That might be fun.

But you're basically still boiling something to make it spin a magnet.