As quoted from the main page:
"Words like 닭(chicken) when followed by the subject marker 이 and the object marker 을 would normally have the pronunciation "달기" and "달글" respectively if they followed the normal rules. However they get pronounced as "다기" and "다글" instead."
Does this occur only with the consonant ㄷ and the consonant cluster ㄺ? If this is so, this anomaly can be explained by the articulatory positions of ㄷ, ㄹ, and ㅏ. Since ㄷ precedes ㄹ during articulation and ㄹ has a similar position for articulation as ㄷ, it makes sense that ㄹ would not be heard. (The sound of ㅏ as a low vowel also requires that the jaw be dropped. If you would take a moment to experiment, you would find that moving the tip of your tongue with your jaw in the position of ㅏ creates very little difference. In contrast, other vowels would not show this quality and would likely exhibit a noticeable appearance of ㄹ.) If its pronunciation is stressed, it is perhaps possible that 달기 (or 달글) would be heard. But in native, fluent speech this sound is slid into during articulation for only the briefest of moments and is thus inaudible.