Very low drop rates of certain "non-rare" corpses in ID
I noticed that certain corpses have extremely low drop rates in the ID, on level 4. For example a karmic lizard or a large snake - over 40 kills in a row and no drop for both. In the same room an orc corpse drops 20-25% of the time.
I know that the probability of drops vary, but at least the wiki has no info on these two being extremely rare (as in gelatinous cube for example) or the ID having reduced drops (as in small cave). Might be rng and bad luck, but the odds seem a bit low.
Character had food preservation (at normal troll starting levels).