The study investigates the impact of glottal elements before word-initial vowels on the speed of processing of the phrases taken from natural continuous speech. In many languages a word beginning with a vowel can be preceded by a glottal stop or a short period of creaky voice. However, languages differ in the extent of use and functions of this glottalization: it may be used to mark the word boundary, for instance, or to add special prominence to the word. The aim of the experiment was to find out whether the presence of the glottal element can influence reaction times in a word-monitoring paradigm. Users of different languages - Slovak and Czech learners of English, as well as native speakers of English - were participating in perception testing so that the influence of the mother tongue could be determined. The results confirm the effect of both glottalization and the L1 of the listeners. In addition, a significant effect of test item manipulations was found. Although the phrases with added or deleted glottal stops displayed no obvious acoustic artefacts, they produced longer reaction times than items with naturally present or absent glottalizations. We believe that this finding underlines the importance of inherent stress patterns, whose alterations lead to the increase in processing load.