Each time I insert the bottle into Dario's mouth, I click. Now, sometimes, Dario does a click with his tongue, a loud, nice 'tchak'. I am trying to shape him so that this is word for "more food, please". It seems to be the simplest possible shaping possible: he gives the cue, I do the behavior.
So far: no success. Need to remember to stop the training after a few minutes into the feeding: he still needs to be hungry enough to pay attention.
But so exciting.