(idiom) a master just shows off a little bit his/her great talent or skill
Definitions (粵典–words.hk)
語句
擁有好高才能嘅人稍微顯露一下佢嘅本事 (of talented people) to show one's talent a bit
煮兩味家常小菜,對佢嚟講只不過係牛刀小試。
煮两味家常小菜,对佢嚟讲只不过系牛刀小试。
zyu2 loeng5 mei2 gaa1 soeng4 siu2 coi3, deoi3 keoi5 lai4 gong2 zi2 bat1 gwo3 hai6 ngau4 dou1 siu2 si3. For her, cooking two ordinary dishes is just to show a tiny bit of her talent.