They may be the product of genetic manipulation or some other advanced technology, as they certianly don't behave anything like real dogs; they are more like tiny furry humans. They don't talk, but that's probably only because they have such disdain for us. They may well be cats in dog suits, but no zipper has yet been located. They look like a cross bewteen an Ewok, a Mugwai and a Hobbit; they have large, round eyes with a gentle, loving expression, which conceals the vast, malign intellect within. They are clever, inquisitive, ingenious and capable of thoughtful malice and destruction. They can look and act VERY cute when they want to, and really know how to work a crowd. They may be related in some way to lephrechauns, as they seem to have a number of paranormal powers, including the ability always to be the wrong side of a closed door.
It is not disputed that for may years, Shih Tzu were the pampered pets of the Chinese Imperial family. As a result of this, Shih Tzu seem to have a racial memory of being carried round on silk cusions with golden tassels, and fed tiny morsels of tasty food by a small army of subservient flunkeys. Since this is what they are used to, this is what they expect. Any Shih Tzu inserted into a "normal" house consisting of adult and immature humans, other dogs, cats etc. will, despite their diminutive size, quickly become "boss" of the entire establishment; they have a Size Twelve personality squashed down into a Size Three body.
It is oftain said by those who do not understand them that Shih Tzu think they are human. This is not in fact correct; Shih Tzu know they are Shih Tzu, but importantly what they also know is that humans are just big pink monkeys placed on this planet to be at their beck and call every moment of the day and night, and to tend to their every whim immediately and without question. When one of their slaves fails to behave as expected, they generally adopt a puzzled, sorrowful look, as if pitying the lack of understanding.
If they do not get their own way immediately, the look of pity is replaced by what can only be described as a Special Paddington Hard Stare, swiftly followed by The End Of the World As You Know It as the docile little furball erupts into incandescent rage at your incompetence.
Depriving a Shih tzu of something it wants (Biscuits, your dinner, the middle of the double bed, the most comfy chair, a go at driving your car) can result in an orgy of destruction; expect linings pulled out of shoes, remote controls hidden under furniture, expensive audio cables chewed through, and puddles of urine on the bathroom floor as a carefully placed early morning trap for the unwary.
On the other hand, Shih Tzu often behave like living Teddy Bears, and enjoy being treated as such. They can be very affectionate and cuddly. Don't be fooled; this means that (a) they have done something bad, and are trying to build up 'credit', or more usually (b) they are planning something, and are lulling you into a false sense of security.
"Oh no.... check under the bed. You know how much Shih Tzu like sucking smelly socks...."