说错了 应该是咬舌尖

in the和 than that是两种情况，in the是n发完之后，舌头向前伸到位就行。
而than that，在发than时，舌位不变，紧接着发that。

此时/n/会齿化，语音学书上的解释是：/n/ before dental sounds /θ,ð/ is realised with a lingua-dental closure [n̪], as in ‘tenth’, ‘when they’—and sometimes when following /θ,ð/ (‘earthen’, ‘southern’).
另外，发/θ,ð/时也未必要咬舌头，请见以下帖子中第4楼的回答。
https://tieba.baidu.com/p/5304710026?share=9105&fr=share&share_from=comment&post_sort=1&post_id=111488930547