What is an example of motif in the novel, While My Pretty One Sleeps?

One of the ideas that recur in the novel is the idea that every killer leaves a calling card. It is believed that once police discover this calling card, it will lead them to the killer. Myles and Neeve, however, disagree as to the nature of the calling card in Ethel's death. Myles believes that his police experience gives his ideas about the case more weight than Neeve's ideas, even though she was the one who created Ethel's outfits and knows there was something wrong with the way Ethel was dressed.

Myles believes that the calling card was the punch that Ethel received to her face from her ex-husband. He has researched Seamus' background and knows he was a boxer in his youth. He suspects that Seamus might not have intended to kill Ethel, but was perhaps so angry at the lady that he hit her harder than he meant to, then cut her throat.