"Is There a Santa Claus?" joke

No known species of reindeer can fly. But there are 300,000 species
of living organisms yet to be classified, and while most of these are insects
and germs, this does not completely rule out flying reindeer which only
Santa has ever seen.
There are 2 billion children (persons under 18) in the world. But
since Santa doesn't (appear) to handle the Muslim, Hindu, Jewish and Buddhist
children, that reduces the workload to 15% of the total - 378 million according
to Population Reference Bureau. At an average (census) rate of 3.5 children per
household, that's 91.8 million homes. One presumes there's at least one good
child in each.
Santa has 31 hours of Christmas to work with, thanks to the different time
zones and the rotation of the earth, assuming he travels east to west (which
seems logical). This works out to 822.6 visits per second. This is to say that
for each Christian household with good children, Santa has 1/1000th of a second
to park, hop out of the sleigh, jump down the chimney, fill the stockings,
distribute the remaining presents under the tree, eat whatever snacks have been
left, get back up the chimney, get back into the sleigh and move on to the next
house. Assuming that each of these 91.8 million stops are evenly distributed
around the earth (which, of course, we know to be false but for the purposes of
our calculations we will accept), we are now talking about .78 miles per
household, a total trip of 75-1/2 million miles, not counting stops to do what
most of us must do at least once every 31 hours, plus feeding and etc.
This means that Santa's sleigh is moving at 650 miles per second, 3,000 times
the speed of sound. For purposes of comparison, the fastest man-made vehicle on
earth, the Ulysses space probe, moves at a poky 27.4 miles per second - a
conventional reindeer can run, tops, 15 miles per hour.
The payload on the sleigh adds another interesting element. Assuming that
each child gets nothing more than a medium-sized lego set (2 pounds), the sleigh
is carrying 321,300 tons, not counting Santa, who is invariably described as
overweight. On land, conventional reindeer can pull no more than 300 pounds.
Even granting that "flying reindeer" (see point #1) could pull ten times
the normal amount, we cannot do the job with eight, or even nine. We need
214,200 reindeer. This increases the payload - not even counting the weight of
the sleigh - to 353,430 tons. Again, for comparison - this is four times the
weight of the Queen Elizabeth.
353,000 tons traveling at 650 miles per second creates enormous air
resistance - this will heat the reindeer up in the same fashion as spacecrafts
re-entering the earth's atmosphere. The lead pair of reindeer will absorb 14.3
quintillion joules of energy. Per second. Each. In short, they will burst
into flame almost instantaneously, exposing the reindeer behind them, and create
deafening sonic booms in their wake. The entire reindeer team will be vaporized
within 4.26 thousandths of a second. Santa, meanwhile, will be subjected to
centrifugal forces 17,500.06 times greater than gravity. A 250-pound Santa
(which seems ludicrously slim) would be pinned to the back of his sleigh by
4,315,015 pounds of force.
In conclusion - If Santa ever did deliver presents on Christmas Eve, he's
dead now.