I tried to teach my son the sign for crocodile at one point and we had a heck of a time. My son let’s me manipulate his hands, not every baby does though so this helped. I’m a touchy feely Dad and touch plays an important role in our silent communication. I find it helps me lead him by example instead of being overly verbose.
So as I taught him the sign, I found that he wasn’t easily able to turn his hands over palm up and palm down like the sign required with hands spread open coming together like the teeth of a crocodile. Instead, he would just clap them together. I assume this is because wrist movements are difficult for a baby to do. As we worked toward the sign with a cartoon image of a crocodile in a book as an example, I’d grab his hands and try to turn them and model the sign for him as he sit on my lap. It was to the point that the sign would look like him pulling his hand up over his head exaggeratedly (him trying to turn his wrists over) and finally coming together in a clap. Amusing to watch but not exactly perfect. This was his version of the sign and he would repeat it whenever the images was shown and eventually with other real life images in other books and on the Internet. Because the sign was used in more than one place, we knew it was in fact a sign. In other words, that’s the real determining factor for a sign approximation. It works across situations and it somewhat resembles the actual sign.