Threshold concepts have been characterised in the literature as jewels in the curriculum as they can inform teaching and learning practices. Therefore, identifying and addressing threshold concepts in any discipline is critical. The aim of the current study is to explore the existence of threshold concepts in computer programming and specifically with regard to the area of functions. Based on our previous works in which we identified 11 potential threshold concepts in functions by employing the Delphi method and seven misconceptions that students hold in this area of programming, the current study further explores computing teachers' experiences with students' engagement with 4 of the 11 concepts using an interpretative phenomenological analysis of interviews. The analysis revealed that from these concepts, we could argue that parameters, parameter passing and return values likely form a threshold conception and procedural decomposition is a procedural threshold (threshold skill). The study presents our framework that lead us to the identification of these thresholds in computer programming, presents the computing teachers experiences with these concepts and concludes with the implication of these results on students' learning and teaching practices in computer programming.