How is Ratchett described in the novel, Murder on the Orient Express?

Ratchett is described as animalistic.

From the text:

When [Ratchett] passed me in the restaurant ... I had a curious impression. It was as though a wild animal ... had passed me by ... The body - the cage - is everything of the most respectable - but through the bars, the wild animal looks out ... I could not rid my-self of the impression that evil had passed me by very close."