How do you get past the spider in Limbo that is behind the tree trunk?
Run up to the spider, and just as its leg is about to do the stomp animation run back. Do this a few times and a bear trap will fall from a tree branch to the left. Push the bear trap to the spider and do the same thing you did before (wait for it to stomp and run away). Position the bear trap so that it hits the bear trap. Do this 3 times (against 3 legs) and you'll beat it.