Taishanese joke

Here’s a joke which works in Taishanese but I think you can figure it out with Cantonese. It doesn’t work in Mandarin:

Ah Ming was known as the class rebel. he was proud of his reputation as the bad boy because he knew very well that the girls love a bad boy. One day in class, his teacher joked about him in front of everyone, which he really didn’t take kindly to, so was angry. It was time to go over some English, so the teacher started testing the students on vocabulary.

‘Now, Ah Ming, how do you say “猫” in English?’ He didn’t know the answer and decided to be defiant, so after ignoring the teacher for a few seconds and avoiding his gaze, with almighty effort and noise, he first gathered the saliva from the back of his throat ‘Kaaargh!’ then spat it out on to the floor ‘Tu!’. For a split second, he was pleased with this show of contempt, until the teacher’s eyes lit up, shocked ‘Yes, that’s right! Well done, Ah Ming!’

Ah Ming was a little confused before assuming the teacher was being sarcastic and was now seething at having been made fun of. After a few more questions around the class, it was Ah Ming’s turn again to answer another question.

‘How do you say the English word for “绿色”?’ To restore his reputation he decided to be rude and really get into trouble this time, so he barked ‘Ghee leen ah!’, only to be perplexed at becoming the star pupil, his reputation destroyed!