Val et al: My first Border Collie (obedience, etc.) knew "speak" and "whisper". We had a hand signal for "speak". Old Daisy was in a couple professional theater productions in Detroit: "Of Mice and Men" where she had to limp and look very old; and "Learn to Fall" where she had to enter and exit on cue, jump up on the bed, etc. AND bark whenever the word "pie" came up in the dialogue.
It went pretty well, with the main character giving her the "speak" hand signal initially, but as the shows run drew on, she took to improvising: In "Of Mice and Men" she recognized the line preceding her exit and started to anticipate it. Since the dialogue discussed the need to take the "old, raddled cur" out and shoot him, it looked a bit odd to see her hop up and start offstage on her own when that line was said....And as to the "Pie" cue, she started "whispering" instead of speaking. So sometimes the audience caught it, sometimes not.
At one point in that production, the main character was sitting on the edge of the bed, dog beside him, and he was typing a story. Talking to himself/the dog, he takes the page out of the typewriter, reads it, shows it to the dog, crumples it up and throws it away. Well, one night he held the page over in front of Daisy, she looked at it, then looked right away to the side. The audience roared with laughter. From then on, whenever the character showed her the paper and asked, "Whaddaya think?" she'd do the same thing and get the same reaction.
Needless to say, BCs are smart enough to learn even what we don't realize we're teaching.
Incidentally, to get her to "whisper" was quite easy: Sometimes the "speak" didn't come out loud and I'd just say, "whisper" in a whisper and she caught on to the difference fairly quickly.
Nancy in Michigan USA