-Having enough suspicion
of a situation or event to the point where
you have to investigate further to see if it was wrong or bogus (or BS).
-Hearing what seems
like bullshit, and checking it out further.
"Tom said he couldn't come
in today because he had an appointment."
"Hmm, that's funny. He didn't mention anything to me. When
back, I want to see his appointment slip to smell check his story."