"Multitasking and Chewing Gum" joke

New Deal software runs in a preemptive, multithreaded multitasking
environment. But what does that mean? Here's an explanation from one
of the designers of the software.
The Walking and Chewing Gum Theory
Single-Tasking: You are walking down the street
and you decide you would like to chew gum. You stop, untie your shoes
and take them off, get a pack of gum from your pocket, take out a
stick, put it in your mouth and then chew. When you are done chewing
you remove the gum from your mouth, place it carefully back inside the
wrapper, put it in your pocket, put back on your shoes and then
continue to walk.
Task-Switching: You are walking down the street
and you decide you would like to chew gum. You slip out of your
loafers, grab the piece of gum you have stashed behind your ear for
just such an emergency and chew, chew, chew. When you are done
chewing, you remove the gum from your mouth and quickly place it
behind your ear (making sure, of course, that no one sees you do
something so disgusting), slip back on your loafers and continue
walking.
Cooperative Multi-tasking: You are walking down
the street with gum in your mouth. Your shoes have been specially
designed to release your brain at the end of every other step. As soon
as your brain is free it notices that you have gum in your mouth. You
chew your gum twice. Your gum then releases its grip on your
brain. Your brain looks around and realizes that you are standing in
the middle of a busy street with your mouth open. You quickly start to
walk, hoping that you will reach the sidewalk before you are hit by a
car and lose your gum. Warning, there may be bugs in your shoes or
your gum. Several users have reported uncontrollable chewing while
standing on one leg.
Pre-Emptive Multi-tasking: You are walking down
the street and chewing your gum. Just like the other coordinated human
beings. Little do they know you are really an android: a flesh covered
machine from the future, stalking the streets of the city, looking for
a haircut.