explain montmorency and his encounter with 'tom' cat

Montmorency loves nothing more then to chase cats. In Chapter Thirteen, he pits himself against a large black tom cat that will have nothing to do with him. The cat just sits and stares, and Montmorency ends up walking away.

From the text:

"Montmorency does not lack pluck ; but there was something about the look of that cat that might have chilled the heart of the boldest dog. He stopped abruptly, and looked back at Tom."