1. There are one or more horses in a scene
  2. We see the (a) crow
  3. Sherlock steps us through something
  4. Sherlock takes a dig at Lestrade
  5. Sherlock conducts an experiment
  6. Sherlock messes with Watson or vice versa
  7. The London Bridge shows up in frame
  8. Blackwood kills someone (either directly or indirectly)