This paper investigates the effect of sentence complexity, specifically lexical and syntactic surprisal, on L2 listening difficulty. Psycholinguistic studies revealed that surprisal cases correlate with textual comprehension difficulty. Based on surprisal theory, these cases are less probable or expected, considering the precedent context, thus require more complex processing to comprehend. Little is known about the influence of the surprisal factor on L2 listening comprehension. We aim to examine this effect and propose to include these cases in captioning to assist L2 listeners. Since conventional captions include the whole transcript, we use Partial and Synchronized Caption (PSC) with limited textual clues, which allows for highlighting surprisal cases to reduce ambiguity. In our experiment, intermediate learners of English (undergraduates) were asked to transcribe and paraphrase videos containing surprisal cases. Results revealed that learners faced difficulty when encountering surprisal, which was partially addressed with the help of PSC, yet more assistance was required. [For the complete volume, "CALL for Widening Participation: Short Papers from EUROCALL 2020 (28th, Online, August 20-21, 2020)," see ED610330.]