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. The third person singular of the same verb is given by way of contrast, to illustrate the verb base.
|l (_V)||dl||nidlat||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 nilgaih. Here the /d/ of the 1d subject prefix /id/ disappears.