There are two situations in which a /d/ comes to be adjacent to the initial consonant of the verb base, namely:
The resulting consonant clusters are treated differently from comparable clusters elsewhere in the verb. The rules governing these clusters are known as the D-Effect.
The following chart illustrates the cases in which /d/ is realized in some way. In all other cases, the /d/ disappears without a trace.
The effect is illustrated here with first person dual verb forms. The /d/ valence prefix behaves identically in terms of its effect on a following consonant. However, when there is no D-effect, an epenthetic vowel is inserted after the /d/ valence prefix, but not after the final consonant of the 1d subject marker, The third person singular of the same verb is given by way of contrast, to illustrate the verb base.
|l (_V)||dl||nidudlat||nulat||float around|
The condition in the case of /l/ is that it be followed immediately by a vowel, that is, that it be the initial consonant of the verb stem. Where the /l/ is the valence prefix it will necessarily be followed by the initial consonant of the stem. In this case, the /d/ is invariably deleted without a trace. For example, the 3s of ``run around'' is nulgaih, with /l/-valence. The 1d is nidulgaih. Here the /d/ of the 1d subject prefix /id/ disappears.