The tinker had something at the tip of his tongue.

修补匠话在嘴边，可就是一时想不起。

The secret which he wished to reveal was at the tip of his tongue and he was not able, did not know how to translate it into words.

他想透露的秘密就在他的舌尖， 他无法，也不知道如何将其转化为文字。