There's that scene in the fourth Act that most people are familiar with, where the weird sisters brew their potion to call up spirits to delude Macbeth. This reminded me of something a former housemate told me once--that she'd read a thesis or scholarly article which claimed that all the horrible ingredients named in that chant were actually nicknames for herbs and things, and that if you actually brewed the ingredients onstage, that it would counteract the curse. I don't know about that, and think it would be pretty hard to do onstage, even in the Elizabethan theatre (which were mostly of wood and straw and prone to burning down), but the idea of herblore being hidden that play is interesting.
Here's some of the possible meanings of the ingredients (but PLEASE don't try this at home--even if they're not actual body parts and such, many of them are still quite dangerous--Monkshood (or Aconite), for example, can kill you just from brief skin contact):
Toad Venom--Bufotenine, thought to be mildly psychoactive; or, the plant Toad Shade (trillium sessile)
Eye of Newt--Mustard Seed
Toe of Frog--Bulbous Buttercup
Wool of Bat--Holly Leaves, Hairy Mullein, or Wooly Faverel
Tongue of Dog--Houndstongue
Adders Fork--Adders tongue
Lizard's Leg--Ivy or Tarragon
Howlet's Wing--Cudweed (called "Old Owl")
Scale of Dragon--Dragon's Blood (daemomorops draco)
Tooth of Wolf--Monkshood
Witches' Mummy--Witch Herb (artemisia vulgaris)
Shark's Maw and Gulf--could be literal stomach and throat of a shark; dried shark's intestines are still sold as food ingredients.
Root of Hemlock
Jew's Liver--Jew's Ear, or Cuckoo-Pint
Gall of Goat--Goat's Rue
Slips of Yew
Turk's Nose--Great Mullein
Tartar's Lips--Sour Cherry
Baby's Finger--Foxglove Blossom
Tiger's Chaudron--Tiger Herb (centella asiatica)
Sow's Blood--could be literal pig's blood
Grease from the murderer's gibbet--Felonwort or Bittersweet
A Hawk’s Heart: Wormwood
Ass’s Foot or Bull’s Foot: Coltsfoot
Bear’s Foot: Lady’s Mantle
Calf’s Snout: Snapdragon
Graveyard Dust: Mullein
Sparrow’s Tongue: Knotweed
My personal take on the Macbeth curse is this--there are a lot of speeches calling on dark powers in this play, mostly uttered by MacBeth, Lady MacBeth, and the Weird Sisters. These are very, very well-written speeches and, delivered by a good group of actors with great energy and strong intention, would be quite powerful. More powerful than a lot of rituals, if truth be told.
I played Lady MacBeth in my 20s in one of my early jobs up in New England. This was also around the time I was seriously starting to practice magic. I remember one night when we rehearsed her first scene, with the speech, "Come, you spirits that tend on mortal thoughts, unsex me here...", over and over and OVER again. I was thrumming with energy as I walked home, and I remember thinking, "I wonder how spirits and elementals and such know that this was a play and not a real ritual," and then it struck me that they probably didn't. And I had just been calling on some pretty dark forces over and over for the past three hours. So when I got home, I did a banishing ritual. And all through the rehearsal and performance period, I did a brief ritual at the beginning of each session to the effect of, "What follows is only a play, please disregard," and another banishing ritual at the end to get rid of anything that might have inadvertently gotten called up. We suffered no ill luck during the entire run.
This could be as superstitious as not saying the name Macbeth offstage, or in the theatre, or whichever variant of the superstition you follow--but I think, if you believe magic is real, that it's not an unreasonable assumption. There really is not much difference between good theatre and ritual, except that in theatre you are evoking parts or forces within yourself, while in ritual you are calling on gods and beings without. Some beings are not that bright and could easily get the two confused.
"Peace! the charm's wound up!"