MHB Logic and Laughter: A Railway Tunnel Experiment

[mathmaniac1]

Three scholars are riding in a railway car. The train passes through a
tunnel for several minutes, and they are plunged into darkness. When they emerge,
each of them sees that the faces of his coll~agues are black with the soot that flew in
through the open window. They start laughing at each other, but, all of a sudden,
the smartest of them realizes that his face must be soiled too. How does he arrive
at this conclusion?

 

[mathmaniac1]

Nobody can do this?;);)

 

[jakncoke1]

he touches his face?

 

[I like Serena]

Since they all start laughing they quickly realize that each of them sees at least one sooted face.

If there were two sooted faces, two of them would see only 1 sooted face.
These two would stop laughing then, knowing their face had to be sooted.

When after a while no one stops laughing, they realize all 3 faces are sooted and they stop laughing almost simultaneously.

When they have all stopped laughing they have confirmation for their analysis. $\quad \blacksquare$

 

[mathmaniac1]

I like serena...:D:D

But only one finds it because only he is a scholar...