The PIE root *H2emg’h- ‘bind’ (cf. Lat. angō ‘press, tie’, Gr. ἄγχω ‘strangle’, Hitt. ḫamank-/ḫamenk- ‘bind; promise’, Skt. aṁhú- ‘narrow’, etc.) is represented in the Slavic languages with the expected Slavic o ablaut grade (cf. *ǫzъkъ adj., *ǫzlъ m., *ǫzti, *zь f., etc.) and also in the “unexpected” e ablaut grade (cf. *-ęz-ti, *-ęzati, *-ęzь f., etc.). This article presents arguments leading to the conclusion that the “unexpected” e ablaut grade may also be of Indo-European origin and that the emergence of the “unexpected” prothetic - may predate the Proto-Slavic system. An analysis of individual members of the word family *ęz(a)ti when compared with the word-formationally equivalent members of the Slavic word families *mélsti ‘milk’ and *st’i ‘cut’ shows that nouns of the type *za with the old acute root toneme and certain unexpected signs of the old acute root in *ǫzlъ (Cro., Cro. Čakavian, Cz., Pol.) and *ǫza (Cro. Čakavian, Rus.) can be explained if it is assumed that the PSl. verb *ęst ęzèšь originally belonged to the same group of verbs as *mélsti mélzešь → *mьlzèšь and expressed the altered PIE acrostatic present *H h 2ḗmg’ - mi : *H h 2émg’ -ti; that is, *H h 2ḗmg’ -mi : *H h 2g’ -énti. The unexpected initial *- before *ę is of hiatus origin [Vondrák 1924, I: 209] and could be explained as pre-Proto-Slavic positionally conditioned phonetics in which syntactic contacts of the type *nu H2ḗmg’h-ti/*nu H h 2g’ -énti ‘and he bind/ties / they bind/tie’ resulted in a hiatus with the loss of the laryngeal that was then filled with the semivowel * > PSl. * just as in intervocalic sequences of the type PSl. *žьrnъe < *-u-es < *-u.-es < PIE *-uH2-es [Pedersen 1909–1913, I: 177].