This took me a few months and I’m fairly skilled at both training animals and working with people to change complex behavior patterns. So this is gonna be heavy on the behaviorism side and somewhat show how little I know about cats in particular. Repeat each step a couple times. if you have trouble with a step, try going back to the previous step and repeat it a few times again.
Make sure the cat knows how to take treats out of your fingertips safely. This is a trick that is actually usually easier to teach an older animal because it requires patience. Start a fun new game where you literally just give them treats from your fingers for doing nothing and the only rule is to not hurt you. Give them up to a normal maximum of maybe 5 in a row depending on the size of the treat. But if they get too excited and hurt you trying to get the treat, yell OW and stop immediately, AND do everything to prevent them from eating the treat you just offered. Eventually they will learn to walk up calmly and gently take it. This is very helpful considering you are about to put the treat near your face.
Give cat treat near your face
Give cat treat in front or your nose.
Swap the treat for your nose at the last second and boop their nose with your nose.
Decide on a word or sound to correspond to their nose touching your nose. I make a noise somewhere between clicking my tongue and kissy noies.
Stop using the treat to directly lead them into the motion and just hold it off to the side so they know it’s there, but instead try to get them to boop your nose just by using your verbal signal.
Hide the treat, but still give it for a successful snoot boop.
Quality Control Moment! It was important to me to get a good firm snoot boop, or no treat. This communicated to the cat that I did really want a full snoot boop, not just face proximity. So I didn’t reward snoot boops I wasn’t sure I felt. Almost always with people and animals you’ll get whatever behavior out of them that you reward (although sometimes with both people and animals it can sometimes be difficult to tell exactly what they’re getting out of it, but I digress), so if there’s a way you do NOT want to be snoot booped, this is the part where you communicate that to the cat. Do not give treats for snoot boops you do not enjoy.
Introduce intermittent reward to fully solidify the behavior. This isn’t actually about your comfort, intermittent rewards are actually more powerful than consistent one (it’s one of the key things that makes negative consequences so hard to successfully implement; any inconsistency is just a highly powerful reward). I usually start with every other, but if you have a particularly clever or stubborn cat you could even skip only every third or fourth treat at first. You then wanna move from there to every other, then start giving a treat only every third time and so on. You’ll never taper the animal all the way off the reward, but you can definitely get it much closer to a “when I feel like it” schedule.
These last two are just cuteness fluff on top of the core trick.
Cross-taper the command into a slow blink. Do this by doing the command and the slow blink one after the other, or by using a verbal command to get the animal’s attention, then utilize the slow blink. After a while, try the slow blink alone. If it’s not working to back to strengthening the behavior, maybe by increasing the treats at least for a bit.
For this last one it’s ideal to have a cat that really likes attention from humans. The more of a human attention whore they are the less repetitions you will need since they will be excited to get pets in place of food. It helps for the other steps to have a cat that is comfortable with humans, but anyone can be a ho for treats. To accept love as payment you have to actually like the person.
Transition from treats to pets. You should already be intermittently rewarding. Keep giving the same amount of treats, but occasionally pet them in their very favorite bestest scritches spot. The one that makes them go bonkers. It’s usually on the head or neck, or somewhere on the spine. My cats is her cheeks, as stated. If they’re a super human attention ho cat sometimes you can even give less treats or even just discontinue giving treats entirely.
Now my cat is like "damn all you wanted was snoot boops and I could’ve been getting prime cheek rubs this whole time???
Translating across entirely different types of cognition (as between separate species) is exhausting.