The requirements are similar for encouraging your baby to sign. First, cause and effect, and the more immediate and consistent, the better. When your baby signs MORE for example, you give them more. Just like the laugh kept the dog going, and the dog running around the table kept the baby laughing, your baby getting what they want more of will keep them signing.
Notice how the play was very short, once around the table, one big laugh. The baby didn't keep laughing, he stopped and waited for the dog to run around the table again. And the dog stopped and waited too. It didn't just kept running round and round the table. It was very percise and consistent. The same thing over and over again. That's what we need to do to when teaching and establishing the sign with our baby. That's why I suggest using small amounts of food your baby likes when teaching them how to sign MORE. Cheerios work well but it could also be a spoonful of food. Give them one spoonful then wait for the sign.
Sometimes when the baby does not do the sign spontaneously, we give up to soon. There's no reward for us so we stop trying. Same thing goes for your baby. If your baby signs MORE and you don't notice and give them more pretty quickly, they will give up trying or the lack of consistency will confuse them. So we have to really be paying attention to our baby's behavior, and we have to lead the activity, not follow. So after you give them a spoonful of food, wait for the sign. If they don't use the sign yet, try showing the sign to them while asking if they want more and see if they will imitate it. If that is not working yet, you can gently take their hands and help them make it. Then quickly give them another spoonful of food. And a clap or two and a cheer help too - the dog and baby sure seem to understood that! Then you keep doing that over and over until your baby starts getting tired or the jar of food is finished! How many times you have to help them depends on your baby and their age. It's a very individual thing. It might be 2 times or 200 times but it in the end, it will happen if you don't give up!
Hope you enjoyed the video - there is nothing like a baby's laughter!