If mistakes creep in or creep into a piece of text, they are included despite efforts not to include them.

A few mistakes always creep in during the editing process. 在编辑过程中总会不小心出几个错。

One or two typing errors crept into the report. 报告中有一两处不易察觉的打字错误。

to gradually start to be noticeable

Doubts began to creep into my mind about the likely success of the project. 我逐渐对这项计划成功的可能性产生了怀疑。