There are 7 finals that have /-o-/:
While Cantonese /-o-/ is usually more open than Putonghua
For example:
| 哥 | 該 | 高 |
|---|---|---|
| go1 | goi1 | gou1 |
| 竿 | 剛 |
|---|---|
| gon1 | gong1 |
| 葛 | 覺 |
|---|---|
| got3 | gok3 |
Since none of /-o -oi -on -ong -ot -ok/ is found in Putonghua, beginners often find this set of finals hard to grasp. For more, see ‘Mastery of Cantonese Articulation – Mastery of the /-o-/ Vowel’.