Hunter X Hunter was a series that had never been very tame. Fights to the death and violence were present from the beginning, even though the gore-factor was never extremely high. Times and youth protection laws change, though, as they did in Japan at the time of the following chapters' release, so two scenes were censored. Both the release in Weekly Shonen Jump and the Tankobon release later on were censored like this.
Once again, the fans had to do the work.

A bit of explanation beforehand: fan-made translations, so-called Scanlations, are perfectly normal in the manga scene. Groups that do this usually work under a code of honor that says they do not translate and release anything that is licensed in their country. The goal of these groups is not to steal the companies' profit, but to make series popular that did not make it out of Japan. These fan translations are one of the scene's keystones. In this case, they helped to create the uncensored version.

For the release of these chapters' scanlations, somebody saw to remove the censorings. Since the censor bars were already only some sort of wireframe, the original image behind those were still visible and it was possible to reconstruct those (except for one scene behind of which the events cannot be made out clearly). There are a lot of rumors about an official, uncensored release on the internet. Some people tell about first editions, both in the USA and in Japan, that are supposedly uncensored. Nobody was able to come up with any hard evidence, so the original images were recreated.

The censoring of the two scenes is, in general, extremely questionable, though. There are more brutal scenes in that same volume, such as a human body being mangled by sea creatures and the lacerated head is shown up close:

Another example is the headless and bloody corpse of a completely defenseless man, killed by the king:

In the end, it is a little mystifying why exactly those two scenes apparently went beyond the limit of what was acceptable.

Chapter 236 - Page 3
As Killuah decapitates his enemy, a black bar was put over the stump in the censored version.

Cahpter 236 - Page 5
Another black bar was put over an enemy's head as a thorn is being rammed through it.

Chapter 238 - Page 15
Presumably no censoring, but it should be mentioned nonetheless: due to the fact that a little bit of the image was lost near the lower edge, some of the breasts are not visible any more.