紛れる

1. Origins, structure, and basic meaning

• Structure: 紛れる(まぎれる) is an intransitive verb meaning to become difficult to distinguish by blending in with other things.
• Basic usage: It describes a white cat disappearing against snow or a document getting lost among newspapers.

2. Common pitfalls and similar expressions

• に marking what something blends into
  • In 古い新聞に紛れて, に marks the material among which the document became mixed. The sentence concerns the document becoming hard to spot among other objects, rather than someone confusing ideas.