This is the 9509th most frequent Japanese word.
紛れ込む
紛れ込む: To slip in; to mix in; to become lost in.
紛れ込む is used here to describe the unintended mixing or slipping of an item into another location.
その手紙は間違って他の封筒に紛れ込んでいた。
The letter had mistakenly slipped into another envelope.
紛れ込む is employed to describe a small animal or entity blending into an area, in this case, a bush.
迷子の猫が近くの茂みに紛れ込んだようだ。
The lost cat seems to have slipped into the nearby bush.
紛れ込む is depicted as an unintentional or unnoticed entrance into a location, here referring to a person entering a room.