One lower level student was writing some answers to basic questions about her and her life. Her answer to ‘Do you live in a house or a flat?’ was ‘I live in a pig house’. I demonstrated ‘p-pig-b-big’ a few times, and she understood and changed her answer. I then told her to look for ‘pig’ on her translator app. I said ‘It’s a big difference, isn’t it?’.
But this is not just one student making one mistake – there’s a genuine linguistics/ESL teaching point her. This student’s language does not have voiced consonants like /b/, but rather unvoiced unaspirated consonants like /p/ (as in spin) and unvoiced aspirated consonants like /pʰ/ (as in pin). She is (and other students from her country, and many others, are) just not used to processing the difference between /p/ and /b/, just as I’m not used to processing the difference between /p/ and /pʰ/.