Using pen and paper to perform long multiplications is the first step of externalizing cognistive processes – but we are more and more on a route to have many external actions being part of our cognitive processes (think of Google for extending our current actual knowledge).
So far, so good, but how about mind? Can that then too be partially externalized?
An example given by the authors is the comparison of the behavior of a ‘normal’ person with a person with Alzheimers disease when trying to find a museum. One uses the information in the head, whereas the other relies completely on things in his laptop.
Next step: can  my mental states be partly constitued by the states of other thinkers?
And then how about an extended self?
And if this is extended out of my person – will interfering with my environment have a moral significance similar to interfering with the person? And are some forms of social activity more like ‘thought’ instead of communication and action?