What diversionary tactic does Christie employ in describing Poirot that might mislead the reader initially?

Describing him as a "ridiculous looking little man" (Chap. 1, p. 3), Christie initially misleads the reader, causing one to believe that if Poirot is ridiculous, he cannot be terribly smart. Such a tactic is diversionary and allows the reader to be lulled into a frame of mind in which a murderer might actually get away with the crime.