Why is Albert Einstein laughing?
The ants in his pants are tickling his atoms.
He just realized that his E equals MC Snot.
A voice in his head told him a joke.
He overheard Gary Johnston call himself a writer.
He has a funny boner.
He is looking into a mirror.
He is practising Laughter Yoga and laughing for no reason.
A doctor just told Albert that vaccines are Safe and Effective.
He is expressing his Theory of Laughtertivity.