Aspiration is a feature of English pronunciation that most learners need to study. It can occur on voiceless plosives /p,t,k/ but it appears in varying degrees. It's particularly noticeable before stressed vowels. Where /s/ appears before the plosive, aspiration doesn't occur so PIE has aspiration [pʰʌɪ] but SPY does not [spʌɪ]. It's also worth noting that /t/ has many allophones, of which aspiration is just one and perhaps not as common as other pronunciations in modern GB/SSB English. I tend t