It’s always busy for the It’s Always Sunny in Philadelphia cast.

Rob McElhenney is ready for the world to see the It’s Always Sunny in Philadelphia side of the show’s crossover with Abbott ...

When “Abbott Elementary” creator Quinta Brunson mentioned the idea of a crossover episode with “It’s ... was Charlie’s illiteracy, which has long been referenced in “Always Sunny ...

The episode, which debuted on January 8, was a crossover with "It's Always Sunny in... Charlie Day, Kaitlin Olson, Danny DeVito, Sheryl Lee Ralph, and Lisa Ann Walter are pictured in "Abbott ...

Essentially, "bird law" is a total non-sequitur played off for laughs to show how out-of-depth Charlie is in the real world. It’s a nice wink to "Always Sunny" fans watching the crossover.

The star of the FX series also admits he was initially hesitant about the crossover concept as 'It's Always Sunny in Philadelphia ... with something funny to do. Charlie Kelly fit so naturally ...

The "It's Always Sunny in Philadelphia" crew is headed to "Abbott Elementary" in the first of two crossover episodes.

We’re closer than ever to knowing a premiere date for “It’s Always Sunny ... (Janelle James) and Charlie (Charlie Day) finally learning how to read. The “Always Sunny” version of events ...