Dear Miss Bonham Carter,

We were at the sea side when your letter came or it would have been answered sooner.¹ I shall be very glad indeed if anything out of my small stock of information can be of any use to M^r Darwin.

My experience is that a dog always puts its ears back when it “grins” or “smiles”   I believe that the grin denotes pleasure and a dog never shows pleasure without putting its ears back. Of course there is a grin that shows rage but in this too the ears are always laid back.

When I say that the grin or smile shows pleasure I mean pleasure of a kind that excites the affections, the sight sound or smell of any one that the dog loves.

Pleasure that excites mere interest, however intense such as that caused by—rats, game, the approach of food, &c., has an opposite effect upon the ear, viz, causes the dog to erect it. You can easily prove this by speaking to a dog that is listening or has its interest otherwise excited in such a manner as to cause the ears to be erected. Directly he hears your voice (if he cares for you) he will drop and lay back his ears into the form that they take in the ordinary expression of affection, but when you cease to speak he will re erect them into that of interest.

I have said all this about the ears because I believe that the “grin” or “smile” is invariably caused by the same kind of pleasure that makes a dog lay its ears back & down.

The grin in its full extent is not common so far as I know, but the beginning of it, viz, a slight drawing up of the upper lip just behind the canine teeth is very common and is always I believe part of the expression that denotes pleasure (of the kind mentioned above)²   Indeed of that expression I should call putting the ears back and down the first important characteristic, common to all dogs, and catching up the lip the second important characteristic, common in a less or greater degree to most dogs of a sensitive & affectionate disposition more especially to those that love the approbation and company of their masters. But I believe that there are many dogs of the most affectionate disposition that have not any sign of this upward contraction of the lip.

With the expression of the eye in some of these canine smiles & its exquisite tenderness you are yourself no doubt well acquainted. One thing more I have noticed which is, that the grin will remain sometimes after the expression of affection has been changed to one of interest and the lip will still be kept up perhaps caught by some of the protuberances above the teeth. If you are going to take your dog for a walk he will grin & put back his ears from affection, then he will prick his ears from interest & excitement at the prospect of the walk and the ears will change more quickly than the mouth.

This is a difficult matter to write about for with me it is so much a matter of mere feeling & I fear too much so for my remarks to be of any service to M^r Darwin. We shall be so glad to see you or your sister if ever you are in this direction & you may depend upon my taking the first opportunity of calling if I am in yours but I am too busy to get out much.

With kindest remembrances to your Mama & sister from both of us³ I am | Sincerely Yours | Briton Riviere

Your note book has for once deceived you I think with regard to your being in my debt