This article is written in response to a message board post on starwars.com that asked the following question:"Why does Ponda Baba's arm bleed when severed by Obi-Wan? In Expanded Universe and the other movies when a lightsaber cuts through someone the skin is melted together and no blood comes out but in Episode 4 Obi wan (in the mos eisly cantina) cuts a guys arm off and there was clearly blood!"
From a medical perspective, the Mos Eisley Cantina scene where Ponda Baba (Walrus Man) gets his arm cut off is actually plausible whereas the "Anakin Split" scene in Episode 3 is totally unrealistic.
Lightsabers do amazing things but they cannot defy the boundaries of physiology. Cauterization is a long-established method of controlling hemorrhage but it has its limits. Electrocautery or laser cautery depend on a combination of factors*:
1. Heat
2. Focus of energy (heat) which is sometimes called the current density - this is a mix of two subfactors:
2a. Frequency of the energy wave
2b. Magnitude of energy involved (aka POWER!)
3. TIME (in contact with substance being cauterized)
4. Presence or absence of liquid material (e.g BLOOD!)
Even the most finely-tuned cauterization unit (e.g. lightsaber) has it's limitations when it comes to vessel size, blood pressure, and balance of factors* previously mentioned. Obviously a saber rates very high in the #1 and #2 factors but often lacks when it comes to factor #3 (speaking primarily of battle and not of "door melting"). In its overwhelmingly popular usage in the Star Wars world, the primary purpose of the saber is to cut. In this capacity, the magnitude of the energy must be extremely high in order to vaporize tissue - this makes it a VERY POOR coagulation (aka cauterization) unit even WITHOUT taking any of the other factors into consideration. If you DID take these one-by-one you'd notice that the likelihood of this weapon cauterizing anything larger than an arteriole or venule (very small arteries or veins) would be remote at best. Therefore, it will be limited when it comes to major solitary vessels, especially the aortic artery and its primary branches. Not to mention that skin and muscle do not "melt" in the sense that they cannot take on a "sticky" liquid form like some would like to propose - although when tissue is cut or is necrosing it WILL become somewhat sticky as the body's own coagulation processes take effect, though this effect is NOT even remotely instantaneous except on the most minuscule level.
One side note - lightsaber cuts SHOULD be relatively painless once the cut is done since the nerves SHOULD be cauterized even with the high energy level... see if you can go through the films and pick out the level of pain response in each saber victim!
Now to apply these principles to some of the more well-known and oft-debated scenes of lightsaber amputations, etc...
First - Obi-Wan vs. Ponda Baba in Mos Eisley Cantina. As mentioned before, this is probably one of the most realistic saber cut results known. If you look at the freeze frame of Ponda Baba's arm you will see that it is severed approximately mid-humerus or possibly as low as the distal third of the humerus. In this area there are at least two major blood vessels whose pressure would keep them from being subject to simple cauterization - even if the right combination of factors were in place for max coag. So the arm should bleed out whatever blood is within the major vessels and the stump should bleed profusely from these two vessels and some passive bleeding from the back pressure in the major veins. Ponda' stump didn't bleed all that much in the movie so not perfect but close.
Second - Luke's amputation thanks to Darth Vader in Episode 5. This too is fairly realistic and dukes it out with Ponda as the most impressively accurate cut in Lucas's original trilogy. The cut is much lower than Ponda's and is likely considered to be distal antebrachium (lower forearm) by most fans. The vessels here are numerous but their pressure and size make them much easier to coagulate - not to mention Luke is holding the arm for much of his banter with Vader after the slice. Who knows? Maybe the 20-30 seconds of holding it make up for the saber's poor coag ability? Probably not, but we'll pretend it does.
Third - Darth Maul dies. Okay - this one lacks realism on only one level: BLOOD. Yes this cut would kill someone, but it would kill from loss of blood only and that loss would be large and FAST. This cut severs DMaul right at the base of the aortic artery before it splits into the twin femoral arteries that we can remember so vividly from Blackhawk Down right? But you cannot sell a movie with an R-rating after the tame gore in the original flicks. Talk about a dive in ticket sales!
Fourth - Qui-Gon dies. Ditto from the Darth Maul story. If the aortic artery doesn't bleed, Qui-Gon doesn't become a ghost. After all, its basically lightsaber hari-kari WITHOUT the twist.
Fifth - Anakin becomes a midget. Hmmm... this one doesn't add up. If Darth Maul died from being chopped in half (his aorta was cut), then Anakin should be a ghost at this point too because the femoral arteries that are the primary blood supply to the legs are only about 1/3 smaller than the aorta itself and there is almost NO drop in blood pressure once they split - we're talking vessels you could fit your thumb into! So when Annie was orphaned from his native legs at the upper thigh level, we're talking MAJOR squirtage folks! Perhaps the coag process was aided by the red hot mess he landed on - unfortunately this doesn't wash only because his stumps weren't flat on top of that stuff.
If anyone wants to send me more examples from the films, I will be happy to elaborate on their +/- as far as realism. I only say this because if you've read this far you're obviously one of the more enlightened Star Wars geeks out there and I wanted to give you space to broaden your horizons a little. Ha!!
On a miscellaneous note, another member of starwars.com made an excellent point that he/she did NOT elaborate upon that COULD make a huge difference in the whole Law of Coag Versus Cut stuff - alien physiology. The member's ID is Tarkin the Ewok - wanted to give props where they are due! Alien physiology in some races/species COULD possibly make the difference in this argument in the sense that IF certain alien types had bodies that were devoid of major blood vessels and were basically walking conglomerations of capillary beds and arteriole/venule complexes, you COULD have a cut and cauterization happening at a medium energy level. These individuals would have to be very small, slow, weak, and basically devoid of movement, but they COULD exist although individuals that fit this description are not likely to engage in battle with a Jedi or Sith. And most of our examples actually come from humans anyways. Too bad Jabba didn't get lightsabered - we could've tested that theory in film!!
