I witnessed this on my way back from a walk yesterday. Stood there and watched the whole thing develop. 3 people walked past whilst this happened and glanced up because I was stood still looking up. They acted like this is standard, shrugged and walked on.
When they did the mouth it became apparent what they were doing. I thought this too about the eyes. They must have turned the exhaust thing off. Plus also from their perspective how did they do it?