《太平广记·卷二百八十五·幻术二》
打开之后，他便钻了进去，旋即化作一只鸟腾空而起，飞入蓝天。
既启之，即以身入，俄而化为一鸟，飞冲天。
After opening it, he got in, and immediately transformed into a bird that soared into the sky and flew into the blue heavens. 
<s>[INST] Kindly elucidate the central themes in this passage in English: 既启之，即以身入，俄而化为一鸟，飞冲天。 [/INST] After opening it, he got in, and immediately transformed into a bird that soared into the sky and flew into the blue heavens. </s>
Kindly elucidate the central themes in this passage in English: 既启之，即以身入，俄而化为一鸟，飞冲天。
user
After opening it, he got in, and immediately transformed into a bird that soared into the sky and flew into the blue heavens.
assistant