Unless you specifically saw it come out, then no... not possible.
If you still um, have it, a picture would be helpful. But parasitic worms don't have legs... so... it must have gotten stuck to your dogs area back there and dropped off when you were looking.
My cat is smarter than your honor student.
Stop Dog Fighting ~ Neuter Mike Vick!
~ RIP Timmy ~ May 2009 - November 6th 2009