What does Hank ask to borrow from Carl in the beginning of Chapter Ten? Why?

Hank arrives early at Carl's office and tells him that he must go by his office before going out to the place he'd heard the sound of the plane. Hank tells Carl that he's going to have to put Jacob's dog down and asks to borrow a gun for the chore. Carl agrees and lends Hank a pistol. Hank is crossing the street to his office as Baxter arrives.