Way to tell what boss is going to spawn?

Is there a way to tell what boss is going to spawn? Are there any small audio, visual, etc. cues? I ask this cause I was playing solo earlier on was black forest and in the interlude before the boss wave I heard my character say something along the lines of "What's that smell?" and the boss ended up being Hanz. I don't know if the line is map specific, or if it really is a subtle hint, but I would hope so.