He took that to mean he was talking to someone named "Arre" or something similar, since a single letter for a name would be silly even by his standards.

"Cuthbert Allgood, though you can call me Bert, most friends of mine do. 'Tis far easier to yell than 'Cuthbert' when I've upset them, and that happens far too often for either of our likings, if you ken it."

Cuthbert was prone to babbling even in the best of circumstances, but it was almost as if he wanted to make up for R's lack of verbalization by offering some of his own. And just because he was a total sucker for the attention, Bert tipped the hat off his head again and rolled it back on just like before.