Rat
One of the most trainable animals of its size, and it laughs when tickled, at a pitch too high for us to hear. Rats need company, so they come in pairs.
Photo by pete. #hwcp, CC BY 2.0
Overview
Rats are the most trainable animal of their size that anybody keeps, and they are the one on this shelf that plainly enjoys human company. They learn their names, they solve problems, and when tickled by a familiar person they produce bursts of 50 kilohertz calls, well above human hearing, that the researchers who found them argued are the rat equivalent of laughter. The same calls appear during play and in anticipation of something good.
The cost of all that is time. They live two to three years, which is the shortest commitment on this shelf and the one that hurts, and they are prone to respiratory disease and to mammary tumours in later life.
Temperament
Sociable with people and with each other, and they should never be kept singly. A pair or a group is the minimum, and rats that live together groom, wrestle and sleep in a heap.
They are nocturnal but flexible, and a pet rat will usually shift toward whenever its people are around. Does tend to be busier and more inquisitive, bucks larger and lazier, and both tame readily. Biting is rare enough to be notable in a rat that has been handled at all.
Care and grooming
A lab block as the base of the diet rather than a seed mix, since rats pick out what they like and leave a deficient remainder, plus fresh vegetables and a small amount of protein.
Respiratory disease is the constant. Most pet rats carry Mycoplasma, dusty or scented bedding makes it worse, and a rat that clicks or wheezes needs antibiotics rather than fresh air. Check for lumps regularly, because mammary tumours are common, often benign and very treatable when caught early.
Living and exercise
Tall, with levels, ropes and hammocks, because rats climb well and use every inch of vertical space you give them.
Out of cage time daily on something they can explore, and puzzles rather than a wheel, since an adult rat is more interested in problems than in running. Avoid wire floors, which cause sore feet, and keep the cage somewhere that gets ordinary household traffic. They are more sociable than the room usually is.
Something here wrong or out of date?