Why did Mrs. hudson call Mycroft a 'reptile'?

I think it was an outburst of disgust for the way Mycroft was behaving that moment. He is emotionless (except for his brother) and due to his position often indulges in deeply questionable means to get things done. read more

I guess this was just an outburst from Mrs.Hudson. Reptiles are of cold blooded nature. In a similar way, Mrs.Hudson calls Mycroft a “Reptile” just to signify that he is an emotionless person. And also she was disgusted about the fact that Mycroft didn’t leave the room even after she had asked everyone to leave herself and Mr.Watson alone. read more

I get it that a reptile is a cold-blooded creature, and Mycroft is full of himself, especially not being able to figure out that Sherlock stubs what bothers him, i.e. the package from Mary. read more