Get it? It’s like "Happy birthday," but without the /b/, so it becomes "Happy Earth Day!"
On an unrelated note, did you know that if you phonemically segment the work mule, it would be "/m/ /y/ /oo/ /l/," because it would be. That's what I learned at school today.
Anyway, back to the Earth Day thing: Let’s hear from Andrew and Vanessa to find out what we can do to help the environment.