Why does reanimated Itachi bleed while using Ametarasu (Naruto, killerbee vs reanimated Nagato, Itachi fight), while no other reanimated shinobi bleed when attacked? For example, Minato didn't bleed when his arm got chopped off, and third Raikage didn't bleed when he got struck by Naruto.
They only bleed under special circumstances, a more notable one being when Itachi started bleeding from the use of Amaterasu.
From the wiki:
Reincarnated bodies do not bleed, except in those cases where blood is needed to perform the Summoning Technique. (emphasis mine)
Reanimated shinobi do indeed bleed when under certain circumstances, such as when the second Mizukage summoned a giant clam:
As we all know, with the exception of those who can access the Rinnegan's Animal Path, a blood contract is needed in order to perform the Summoning Jutsu. However, reanimated Hiruzen Sarutobi and the second Mizukage are able to perform this technique while using a blood contract. This is because reanimated are able to attain it (their blood) in certain cases, like the ones mentioned above.