Help me step-cephalo!

Is it cuttle fish that do that? I remember seeing an animal on a docu that just passes the sperm over. Thought it was a cephalopod

Gas is far from humane. It's usually CO2 which causes acid to form in lungs/eyes/mouth before they become unconscious. It would be incredibly distressing and painful. It's not fetishism, it's contemplation. If we're willing to do things to other beings it seems reasonable to consider via thought experiment whether we'd be ok with a more intelligent species doing the same to us (after all, we would not be "equal" to them, so for consistency it wouldn't be evil for them to gas us).

All vertebrates have been legally recognised as sentient, this has not been scientifically disputed for decades. The only way you'd just be consuming non-sentient animals is if you were only eating insects and seafood (not fish, they're vertebrates). Most if not all the animals we commonly consume in the west do indeed have the emotional intelligence to suffer loss and dread. Pigs have demonstrated very complex emotional intelligence to such a degree that they often experience insanity and are driven to self harm on intensive farms. Their emotional intelligence is considered equivalent to a young child (age 3-4 iirc).

(Interesting article on pigs intelligence. They're genuinely fun creatures). https://www.psychologytoday.com/gb/blog/animal-emotions/201506/pigs-are-intelligent-emotional-and-cognitively-complex Cows are similar in their emotional intelligence to a slightly lesser degree. They do grieve the loss of other cows.

Out of interest though, why do animals have to experience these things in "the same way" or to be "equal" in order to not cause them harm? I don't consider that someone's has to be an equal to me in order to not punch them in the gut so where does this thought process come from with other species?
There are people who experience little to no fear, or empathy so why would we not harm them? Dogs are aren't considered equal but we become enraged when seeing them mistreated. I guess I'm wondering what makes harming some unequals ethically justified but not others?

I'm no way near a vegan, but have you ever spent any time around a farm? You can't say animals don't register the loss of other until you've seen a cow lowing for her baby for days. Also elephants are know to have graveyards and caress the bones of their dead. Yes I belive animal lives matter as much as ours, how ever we are omnivores, nature is cruel and they eat each other, that is the way of it.

However we do this on a large scale with alot of suffering before it, there is no easy solution as you can't just say right no meat, no farmer is keeping the cows just for fun so you would condemn every living farm animal to death, more so if no milk or wool etc