People can discern wether a plosive is /p t k/ by formant transition of a vowel. While how do people discern them, if it is a consonant cluster of few plosives without any voicing, as [pt] or even some voiceless random sequences such as [ptkpktpkpt]?
Richard Wright discusses this w.r.t. Tsou, which has a number of initial stop clusters, e.g. pka:ko "to escape", tpihi "mend cloth" (and other kinds of clusters, but stop clusters are the most challenging). There are a number of strategies for making consonants without vowel transitions perceptible, and in the case of stop clusters, there is a high-amplitude release burst between the consonants, which carries sufficient information to allow identifying the pre-consonantal consonant.