In the Discworld universe, when an Igor (which is basically a parody of Adam from Frankenstein) speaks, they generally speak with a lisp (pronouncing "s" as "th").
In Monstrous Regiment, though, when
Igor is revealed to actually be Igorina,
She says that Igorinas don't lisp as much as the boys:
"Sometimes, you forget to lisp," said Polly. "But mostly... it's just a feeling. Little things about the way you move, maybe."
"The word you're looking for is 'Igorina,'" said Igorina. "We don't lisp as much as the boys. It's a style thing."
Monstrous Regiment, page 144
What does "it's a style thing" mean? Why would the Igorinas not lisp while the Igors do?