Mr. Betteredge employs animal metaphors and verbal irony to describe the "wicked Colonel" John Herncastle in Chapter 5 of Period 1, implying to the reader that he is vicious, instinctual, and fierce:
They are very strict in the army, and they were too strict for the Honourable John. He went out to India to see whether they were equally strict there, and to try a little active service. In the matter of bravery (to give him his due), he was a mixture of bull-dog and game-cock, with a dash of the savage. He was at the taking of Seringapatam.
There is a sense of insincere, comedic restraint in Betteredge's descriptions of Colonel Herncastle in this passage. Betteredge calls Herncastle "one of the greatest blackguards that ever lived" just before this. However, he goes on here to refer to him by the sarcastic nickname "Honourable John." Of course, someone who is a "blackguard" is not honorable at all, which is why the verbal irony of this misnomer is so effective. This sarcasm continues in his description of Herncastle's time in India as a way of seeing if "they were equally strict there": the idea that the British Army would be more lenient in some places is an unlikely one.
In saying that the Colonel has "a dash of the savage," Collins uses the metaphor of animals trained to fight to death in betting arenas to characterize Herncastle. "Bull-dogs" and "game-cocks" were chosen for their savagery, and so, he implies, Herncastle is savage by nature.
The word "savage" here is also a pejorative reference to the native Indian population that Herncastle goes to India to try and subdue. The "taking of Serangitapam" was a famously violent suppressive military action by the British in colonial India. As Collins immediately refers to this battle after Betteredge's animal metaphors, it's unclear whether he means the "dash of the savage" he says Colonel Herncastle has in place of "bravery" is an Indian or an animal trait. Given the largely negative depictions of Indian characters in this novel, it seems likely to serve both purposes.
