I had forgotten this but saw the Poirot episode again at the weekend in which it occurred.
Poirot, Hastings and Miss Lemon are taking breakfast somewhere on the south coast. Two boiled eggs are placed in front of Hercule.
He carefully tucks his napkin into the space between his shirt and his throat, puts on his pince-nez, and surveys the eggs.
" I cannot eat these eggs. They are of a completely different size."
Excellent attention to detail.