How does Fangs save Jack from certain death?

Jack tripped and fell into a pit of mud (slime), likely similar to quicksand. Fangs pulled him free and saved his life.

`At last who should appear but my faithful Fangs! He knew my voice and came close up to me, right over the swamp, but all the poor beast could do, was to help me to make a row; I wonder you did not hear us! The very rocks rang, but nothing came of it, so despair drove me to think of an expedient. I cut down all the reeds I could reach round and round me, and bound them together into this bundle, which made a firm place on which to lean, while I worked and kicked about to free my feet and legs, and after much struggling, I managed to get astride on the reeds.

`There I sat, supported above the mud and slime, while Fangs ran yelping backwards and forwards between me and the bank, seeming surprised I did not follow. Suddenly I thought of catching hold of his tail. He dragged and pulled, and I sprawled, and crawled, and waded, sometimes on my reeds like a raft, sometimes lugging them along with me, till we luckily got back to terra firma. But I had a near squeak for it, I can tell you.'