The topic in the textbook was emotions and one of the questions was ‘Do you enjoy horror movies?’. One student said yes, so I asked for an example. He said ‘Saw’. Another student said ‘But that’s an action movie’. He and I looked puzzled. He quickly searched for an image of that movie and showed it to her. She said ‘Oh, I thought you said /sɔ/’, then quickly searched and showed us an image of Thor.
/θ/ is one of the last phonemes which native English speaking children acquire (indeed, some don’t acquire it (and /ð/) at all – dis, dat, tick and tin are part of several established varieties of English), and it is probably the hardest phoneme for second language learners (/ð/ is at least far more common, in higher-frequency words like this, that, these, those, there, then, mother, father, brother).
I’m surprised that this misunderstanding happened this way around. I would far more expect the first student to mispronounce /θɔ/ as /sɔ/. Anyway, the misunderstanding was cleared up, and I was able to give them a brief explanation.