Show:

* give an architecture walk thru

* give a directory walk-thru

* show the hot modules. something like

  git log --pretty=format: --name-only | sort | uniq -c | sort -rg | head -10

* if can generate a dag of module dependency, that would help

* walk thru of the test cases

hands on:

* Ask them to add log messages at strategic places (find needle in haystack)

* Add new test cases in areas with low/no coverage

both are very low risk ways to get familiar with the code base