Troikas: a creative, simple, challenging puzzle

Lightening the mood a little bit today with a simple puzzle called a Troika which I like because creating them is relatively easy, fun, and creative, and solving them can be challenging and also creative. The idea is simple: find what these three things have in common. ("They're all nouns" may be true, but the correct answer is generally the most limiting possible answer.) An example is the best explanation: blue, straw, rasp. This is a pretty easy one: kinds of berries. A much harder example: key, bridge, string are all parts of a violin.

Try these, and post your answers in the comments; some of them are very challenging.

• painting, water, sword
  
• cherry, sky, jet
  
• mail, stink, smart
  
• pig, ink, baby
  
• sterile bandage, photocopier, facial tissue
  
• stiff, Joe, slob
  
• brain, staghorn, reef
  
• brown, peppermint, rerun
  
• bell, ball, mason
  
• addict, sailmaker, phonograph
  
• welt, child, price
  
• stuffed lobster, tamale, deviled egg
  
• pool ball, skunk, flag
  
• tumbler, sun, reading