3週3日目 かじったとたん
Development・time・result
接続：Vた＋とたん（に）
Right at the moment of doing A, B was surprised
注意 / Note：とたん is an immediate sudden change; あげく usually ends badly; 末 is the result after long deliberation; かと思ったら emphasizes two things that follow very quickly.
比較 / Compare：Same article: 〜あげく／〜末に／〜かと思ったら. These models are often mistakenly chosen for each other — carefully read the 接続 and nuances above and then decide.
よく出る形 / Common form：動た形＋とたん（に）、〜。The latter part is something UNWANTED, that happened - do not use the sentences will, order, or inducement.
外へ出たとたん、雨が降り出した。
As soon as I went out, it started to rain.
薬を飲んだとたん、眠くなった。
As soon as I took the medicine I felt sleepy.
席に座ったとたんに、名前を呼ばれた。
As soon as I sat down on the chair, my name was called.