A while back I was often overtaken on my commute by a pickup with a bloody great dog in the passenger seat. The dog would have his entire head out of the window and bark repeatedly, normally I'd hear him coming but he did catch me out a couple of times.
Otherwise passengers shouting is pretty common in my experience- although usually only when the weather's nice, and usually in the evening.
I've had one passenger lean out and give me a shove while I was taking the lane (as the road had no pavement or verge- just a brick wall on the left of the carriageway).
That whistle looks interesting.