why george face changes as he come to know that real truth about shirt?

George thought the fact that the shirt had fallen into the cold, morning water was funny...... until he realized it was HIS shirt.

"It isn't my shirt—it's yours." I never saw a man's face change from lively to

severe so suddenly in all my life before.

'What!" he yelled, springing up. "You silly cuckoo ! Why can't you be more careful what you 're doing ? Why the deuce don't you go and dress on the bank? You're not fit to be in a boat, you're not. Gimme the hitcher."

I tried to make him see the fun of the thing, but he could not. George is very dense at seeing a joke sometimes."