First, a vocabulary lesson. The humor in this comic is called a “mondegreen,” which I wrote about in the past. Good old Frazz.
The other one is a reminder about the rules in Scrabble: Acronyms are not allowed. HOH is the structural formula for water. We laypeople usually use H2O. Thank you, FoxTrot.
Annnd a bonus, because it’s an inside joke. Note also that the company sign also points inward, not out, to potential customers. Well, maybe it’s an inside wall, not a window.