One of my students is someone that studies at a private school taught entirely in English. She needs extra help with her English, so I’m her tutor. I work at the school in an intensive one on one class to help her through her homework. She supplies the study material (Her homework or recent classwork for review), and we go through class working on what she needs to get done.

Today we were reading a story about firehouses. In the story, a group of students visit to see where firefighters work, what they do, and how they protect the community. As the students in the story were walked around the firehouse, they encounter the dalmatian named "Spot".

The sentence in the text was written:
"As Spot ate, the children walked around."

My student has the habit of ignoring punctuation, which causes a weird sense of flow and unnatural pauses that native speakers do not have. Normally this has no affect on the meaning of the sentence itself, but is simply something we repeat and try to fix as we read. Today was the exception, as she read the sentence as:

"As Spot ate the children walked around."

This radically changes the meaning of the sentence. Trying to explain why that comma meant that Spot went from "a dog eating dog food" to a "dog eating children" was hard to explain. The student didn’t really understand how the comma altered the sentence meaning. After all, it’s not a word itself, but groups words and ideas into logical parts. It’s just another way to emphasize that pronunciation and pauses when reading are important.