in reply to Guess what it does ... and a challenge

This does it slowly and is one character shorter than the one you gave in your spoiler:

1x~sleep 9

Update: Btw one could try this (CAUTION! DON'T TYPE BLINDLY!):

but it doesn't work, because
it fills up your disk instead. With GNU Coreutils, you can use the TMPDIR env-var to override where it puts its temporary files. Eg.
[am]king ~$ TMPDIR=/dev/shm/ time perl -we '`yes|tac`' tac: /dev/shm//tacck0ml6: write error: No space left on device 11.48user 2.56system 0:14.05elapsed 99%CPU (0avgtext+0avgdata 0maxresi +dent)k 0inputs+0outputs (0major+1382minor)pagefaults 0swaps

Update: On the other hand, this works, and is shorter than the first one:

Update: the following works too and is even shorter:

Update: and one more character shorter is:

Update: the following has the same length as the first one in this node, but is a slower than that: