Even NTs make mistakes. I remember last year during a training course for work, we were going through the answers on a worksheet we completed. The tutor was funny and jokey and everyone liked her. When we got to one of the questions, after a few seconds of discussing the question, the tutor joked about the answer, and some of us (including me) knew she was joking, while half the group looked down at their papers worriedly. The tutor had to tell them that she was only teasing, and they were like "oh", then laughed at themselves for misinterpreting the joke.
Also I think all NTs take those figure of speech things literally when they first hear them, especially children. When my NT cousin was about 10 she was teasing me about something, and I said "stop pulling my leg", and she said "how am I pulling your leg? I'm not even touching you", so I had to explain to her what it meant, and she was pleased that she had just learnt something.
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Female