I suspect the question was more about the similarity in pronunciation, especially for an untrained ear.
And the answer to that should be in positional context, ie. "das Huhn vor im Bus." would not make sense grammatically. First, it lacks a verb to complete the sentence as is. Second, "vor im" is also improper.
However, "das Huhn vor dem Bus" looks like a possibility as a part of a more complex sentence.