Hey [emoji][emoji] I'm chinese and hope following could help u . In chinese ,嘲笑means laugh at someone .However ,for v+了+v ,such as 笑了笑 Basically , this kind of phrase not only deliver the form of action but also deliver the length of time that actions sustain。Here，笑了笑means，he just smiles for a while ,up to few seconds .But if it is 大笑，or捧腹大笑，stands for something really funny that u just can't stop laughing . In addition， "smile "(微笑)in chinese means that someone just smiles slightly , don't even make any noise or leak their teeth .Smile to others is more polite .

Q1 Does the above sentence mean she "laughed" at me or "smiled" at me? A1 Yes, it does mean that she smiled at you. Q2 If I did not repeat 笑 and left the sentence as 她对我笑了。Would it still be correct and does it mean any different now? A2 It's still the same meaning. Actually, if you repeat XIAO, it's inclined to informal use. Q3 How do Chinese speakers differentiate "laughing" and "smiling"? A3 Laughing = 笑(v.) smiling=微笑(n. and v.)

V+了+V pattern 起到"了"字的作用 由於若不加"了"字，以動作做語意中心的句子（大多）不算完成，這是本地人的習慣約定，沒有任何理由。 加"了"字前，只有V（動作）與主語，可能像＂話沒說完＂，好比英文的I fly / I beat，又可能在＂話沒說完＂下，像過分強調將要做的某動作的驚嘆句，好比英文的I , run!!! I , fly!!! V+了+V pattern整體作用１： 只加上"了"字，即使語句表達完整了，但缺少內容的敘事仍然可能像未完成整句話，像問題中的1,3,4三句話，他撓了頭、老師拍了桌子、孩子哭了，三句話都像是有話題重點尚未講出，而第2句＂我擦了桌上的涂鸦＂就像講完了。（這有關社會經驗而無關本地語感。） 加上完整的＂V+了+V＂pattern後，上面語句中都有了填滿了整句話表達重點的感覺。（為什麼有這種作用？這沒有特定理由，只是本地人語感上的共識） 作用２： 加pattern後，使V（動作）不能表達是猛烈做出的，可能表達輕描淡寫的意味，或表達只是做了一兩下沒做完的V （為什麼有這種作用？同樣沒有特定理由，只是本地人語感上的共識） 他點頭／他點了頭，可以是很戲劇化的點頭 他點了點頭，只能是平常的、或微弱的點頭 他擦了黑板：把黑板擦完了（一般理解） 他擦了擦黑板：隨便甩了一兩下（很可能表示）擦完了整個黑板（不太可能表示） 作用３： 加pattern後，經常表示做的動作有一小段持續時間，或重複動作。 他跳／笑了：只跳／笑了一下 他跳了跳／笑了笑：跳／笑了幾下 ＊笑，smile或laugh都可能，區分的辦法是看用什麼修飾笑字，帶入現實情況。 smile是不出聲的笑、微笑，laugh是出聲的笑、大笑

v了v refers to the action lasted a short time or the action happens for just once. 笑了笑 then means to smile for a little while (not to keep smiling). also, 挠了挠头 means to scratch his head for a bit. Usually, v了v is used together with another action, either as a predecessor or a successor , it rarely forms a sentence by its own.