Punctuation Saves Lives

Punctuation saves lives! What? How come? Yes. Here is the example:

Let’s eat kitty. (Meaning that, we will be eating a cat.)

Let’s eat, kitty. (Meaning that, you and your friend kitty will be starting to eat.)

The above example is a punctuation rule. Your tutor would put it formally like this:

Use commas to set off the name, nickname, or title of a person you have directly addressed.

More Examples:
Yes, old friend, I will.
Good day, Captain.