Why didn't the police or the school pick up on the killers' warning signs?
2011 May 11, Arthur S. Brisbane, "The Other Torture Debate," New York Times (retrieved 24 May 2011):
Readers and bloggers alertly picked up on the nuances of language, and what some called the inconsistencies.
(transitive,idiomatic) To continue or build upon (for example, a task, analysis, or narrative), beginning from a point at which someone has previously stopped.
Andy Murray has landed in Valencia for next week’s ATP tournament to pick up on his interrupted year, six weeks after the Davis Cup tie against Poland when he played three times in successive days and exacerbated the damage to his left wrist.
(transitive,idiomatic) To adopt a practice in which others already engage.
2004 Sep. 16, Patrick Saunders, "Eye on the Jaguars," Denver Post, p. D10:
"What you've got to do is, you've got to study the guy and try to pick up on his techniques, try to pick up what he's real good at."