The term "snake in" typically refers to an unexpected or deceptive presence, and there are many synonyms that can be used to convey a similar meaning. Some possible options include "intruder," "trespasser," "interloper," "mole," "spy," or "saboteur." Each of these words suggests an element of surreptitious action or subterfuge, and could be used to describe someone or something that has infiltrated an environment without permission or knowledge. Ultimately, the choice of synonym will depend on the specific context and intended tone of the communication, but any of these options could be suitable for conveying the concept of a deceptive or unwelcome presence.