Potato to sweet potato. What stem?

This is the transmitter code of the enemy spy in the anti-spy movie Soul of the Sea.

The original words in the movie are "sweet potato, sweet potato, I am a potato". The corresponding code name is the Yangtze River, and I am the Yellow River.

Now it is usually a joke between friends, and because potatoes and sweet potatoes are of the same kind, there are such jokes. Code words between friends are often used for joking, while acquaintances use them more.