A centipede was happy quite,
Until a frog in fun
Said, “Pray, which leg comes after which?”
This raised her mind to such a pitch,
She lay distracted in the ditch
Considering how to run.
If you take your own fun seriously, you might like to follow this implications of this bit of whimsy (by a Mrs. Edmund Craster, 1871) into a branch of psychology not even dreamt of when it was written, cognitive behaviour theory. Start here.