THE GHOST SQUIRREL IN THE MACHINE (SOLUTION)
If you're finding this page randomly, please visit my original blog post to find out what the story/setup was (now that you've ruined it for yourself by seeing the secret surprise ending).
The image above shows the real configuration of the dryer, chipmunk
(turns out the squirrel-thing was a chipmunk) and the exhaust pipe. We
had tried to find the 'squirrel' by removing the pipe and pressuring it
out, but the chipmunk had hidden in the back of the dryer itself. We
assumed that a squirrel would try to make a break for freedom as soon
as it was capable of doing so, but the attention-shy chipmunk chose to
camp out in the perceived safety of the exhaust pipe cave.
Even though we had actually turned on the dryer after having 'verified'
that the squirrel was not in the vent the first time (I know, I KNOW,
I'm sorry), the chipmunk still chose to hide in the dryer when we went
back a second time and discovered what had happened. I eventually got
the chipmunk out by reattaching the plastic vent, waiting until it was
trying to make the impossible leap up the metal tube, then quickly
detaching the bottom of the plastic vent and placing it into our
chipmunk-catching box. We used the cardboard box for a chair for this
purpose which was about 60 cm high, and this turns out not to have been
overkill as terrified chipmunks can jump rather shockingly high.
In the end, the chipmunk was freed and ran away in apparently good health.