What would it be like to be a thinking rock ? A thinking rock is simply a rock endowed with one special ability, that to think. Otherwise it is similar to a normal, non-thinking rock.
Being a thinking rock may be excruciatingly boring. A thinking rock has no senses, and no ability to move or even act. In a sense, being a thinking rock is akin to trapping a mind inside a special prison, a small dark cell where one has neither freedom nor knowledge of the outside world. It is a depressing situation. Two possible real-life analogues of being a thinking rock are i) being in a coma and ii) being trapped in a sensory-deprivation tank.
If we had the prior experience of sensing and acting, being a thinking rock would be a deadening hell. But what if we had no such prior experience ? What if we were born as thinking rocks ? Would our experience of being a thinking rock change ?
The question is beyond my ability to answer. But I believe that the mind of a thinking rock would be significantly different, if not downright alien, to our human conception. For one, a thinking rock may not even have a sense of self. Without senses to percieve others, there is no distinct self. In fact, the mind of a thinking rock is essentially a universe comprising of nothing but itself. To a thinking rock, nothing exists but itself.
Actually, a thinking rock is really nothing more than an analogy for an absolutely abstracted mind, free of any associations with the 'real world'. It cannot sense nor interact with the 'real world'. This absolutely abstracted mind is a distinct possibility if mind-matter duality exists.
But that is another discussion for another day.
Til then, just convince yourself that thinking rocks do not exist.