This study investigates the use of L1 glosses during computerized reading in the English Language Teaching (ELT) context. A group of 26 ELT students at a large Turkish public university read three short texts and used pop-up glosses to promote their comprehension. Web pages were designed for reading and glosses, and a screen capture tool recorded the participants' onscreen actions. The glossed-items that the participants clicked were examined for word-type selections to see whether the clicked items were useful, high-frequency words in the main parts of sentences or if they were in the supporting details. Three nonsense words replacing three main lexical items were also employed to observe the students' purposeful clicking to understand the texts. The findings indicated that ELT pre-service teachers were careful and meticulous in their selection of look-ups. However, there was a discrepancy between the words that students claim to know and the words that they actually checked during glossed reading. The study confirmed the tendency for more look-ups with pop-up glosses as mentioned in the literature, even though the glossed items were not visually enhanced. The genuine look-up behavior was also confirmed with the moderately high clicks on the nonsense words. We can conclude that trainees are able to determine the types of words to be checked for better text comprehension but they seem to need training and more practice for using other strategies other than relying solely on gloss-type information sources. We suggested implications for further studies.