there has been an ongoing study. Hunger for Words | Meet Stella, The World's First Ta... this one was the first one, but then more scientists got into it and created a specific format for the buttons and it is now a business
buttons can be found relatively cheap in Amazon or Aliexpress but the fluentpet layout is v clever and makes it easier to add buttons and also for the dog to know what a new button means when they're introduced
I know cats are also smart enough to do the button thing but what owner is masochistic enough to listen to infinite "food food food food" calls at 3 am
one of my plurk pals has some for her border collie! iirc he especially likes combo-ing "walk" and "mad" when the weather is too nasty to go for a walk lmao