pick up on vs undertake

pick up on

verb
  • To continue or build upon (for example, a task, analysis, or narrative), beginning from a point at which someone has previously stopped. 

  • To adopt a practice in which others already engage. 

  • To notice, observe, learn, or understand, especially something otherwise overlooked. 

undertake

verb
  • To take upon oneself; to start, to embark on (a specific task etc.). 

  • To commit oneself (to an obligation, activity etc.). 

  • To pass a slower moving vehicle on the curbside rather than on the side closest to oncoming traffic. 

noun
  • The passing of slower traffic on the curbside rather than on the side closest to oncoming traffic. 

How often have the words pick up on and undertake occurred in a corpus of books? (source: Google Ngram Viewer )