From Arthur Nicols   18 January 1878

My dear Sir.

Some time ago I mentioned to you that my landlord, who is a practical gas-fitter etc, had told me that he had then recently been fitting a new leaden pipe to a cistern, the old one having been perforated by rats and rendered unserviceable—the object of the animals being to obtain a regular supply of water.¹ He has now obtained an excellent specimen for me which I will send by post if you would like to see it. It was taken from under the flooring of a house in this neighbourhood, and was the permanent source of supply for probably hundreds of rats—the occupier of the house complaining of the great numbers always about the house. The specimen shows an attempt to cut the pipe longitudinally and then abandoned, next a great deal of waste power in attempting a transverse section, a mere pin hole being the result, finally a determined transverse attack—probably by a single rat, the impressions of the tooth being of exactly the same width, resulting in a hole of this size and irregular shape.

Absolute proof that this is the work of the rat is afforded by the fact that several hairs are imbedded in the lead where the partially successful attempt was made and one of these is, I think, a vibrissa. It is conceivable that these hairs were rubbed off the animal’s skin and fixed in the lead by small strips of the metal laid over them in the act of gnawing.

You suggested I remember that they hear the water trickling and are thus led to attempt to reach it.² I am only too glad to accept this explanation, because it sustains my conviction that animals reason from observation, and that the mental operation is identical with that some of us make so much fuss about, as if it were our exclusive possession!

Yours faithfully | Arthur Nicols.

Chas; Darwin Esq. F.R.S