What potential “harm” could occur to a research subject? How does a researcher minimize harm?

What potential “harm” could occur to a research subject? How does a researcher minimize harm?

This is a discussion post question. Plesase use this reference or one like it to respond http://www.american.edu/irb/IRB-Training.cfm

What potential “harm” could occur to a research subject? How does a researcher minimize harm? What should a researcher do if harm does happen?

This does not have to be long and it does not have to be in an APA format