Trying to answer this Q, I just re-watched the HD version of ROTJ and noticed that Jabba the Hutt had an injury on his tail.
Originally, I thought it was from a blaster bolt shot by Luke as he was dropped into the rancor pit, but then I saw that it was there even before, when Luke just walked in (also, Hutts' skin is supposed to be proof against blasters).
Is there any information in Legends or DVD extras that explains how Jabba got his tail injured?
(Note: I considered that what I think is an injury could be some part of Jabba's Kowakian monkey-lizard body wrapped around Jabba's tail. But judging by Jabba's skin movement; as well as changing position of monkey's hand, it's a tail injury).
You can see it clearly in 4 scenes (in decreasing order of detail):
~29 minutes into the movie, where Jabba decrees via C3PO that all the heroes are "to be terminated" by Sarlacc:
~25 minutes into the movie, when Luke is down in the rancor pit, and Jabba's entire platform gets moved so he can see this better (right after Lando exchanges glances with Leia)
~24:15 minutes into the movie, when Luke tells Jabba that "you will bring Captain Solo and the Wookiee to me".
~22:44 minutes in, when Jabba is asleep as Luke enters his gates and chokes the Gamorrean guards