Answer:
Yoni's description shows that he looks unusual and for Sergei. While the words "knocking" and "rapping", show how evasive Yoni was in Sergei's life causing something of great influence.
Step-by-step explanation:
Sergei is not an Arab boy like Yoni, which shows that Yoni may have unusual customs and looks for Sergei, like wearing an earring, something that draws Sergei's attention because he is different and exotic.
Yoni has a very big impact on Sergei's life, as Sergei accidentally kills him because he thinks Yoni tried to catch his magic fish. This impact can be shown by the words "knocking" and "rapping" that give the feeling that something invasive, loud and disconcerting is happening.