Before Entulmir died for the first time they had been kept in one of the orc factories for a while.
(By then Sauron had standardized whole sets of procedures to effectively turn baby elves into orcs. Older elves tended to go crazy or die; children’s souls and bodies were highly moldable because they did not really know what they would be like in adulthood. It was always easier to train them into their roles when they had little life experiences and self image.)
What happened should be pretty bad, at least bad enough to make them either forget most of the experience or only remember things in a completely disassociated way.
Years later they could casually recite to Este’s Maiar “I think they poured something hot or acidic or both under skin to dissolve the muscles. It was slow and very awful; the thing had a consistency of melted sugar… Or I might be having a particularly bad fever and was hallucinating all the time.”
Which wasn’t any good reliable information at all, but still way better than what one can get questioning ex-orcs in the Halls. (Some of Este’s Maiar got ages-long ban from Mandos by Morowe for a reason.)
One important thing about the creation of orcs was the subject had to somewhat believe they were not an elf. They either didn’t think they could be an elf ever again, or didn’t remember they were once an elf, or didn’t want to be an elf, or didn’t even think about the matter because thinking meant a lot of pain.
(Orcs were sad abnormal creations because every orc, even the one that born as orc instead of being turned, lived with this feeling of wrongness all their life. Like their body were not wholly their own; they were supposed to look like something else but they did not know what it should be like. They were supposed to be immortal due to the elf origin but they were not. It was like having slow progressing illness that consumed their body and mind bits by bits.)
(Orc mortality was not a natural one. Elves did die of physical or mental illness. Being an orc was like, you get this long term condition that constantly wore down your soul and body. There were ways to ease the pain but no cure.)
Most of the early orcs in the Halls did not remember anything at all. Or they tend to get into mental breakdown and start to hurt themselves when getting reminded of the experience.
Entulmir considered themselves very lucky to have themselves killed before reaching that point.
(Slowly dissolving in an icy river for years afterwards helped too.)