(NOTE: Sorry about the audio; a fixed version will be uploaded as soon as I have finished downloading it)
When Applejack saves Spike from a timberwolf attack in the Everfree Forest, he insists on helping her around the farm in order to repay the life debt he feels he owes her. His efforts only make trouble for her and the other ponies, and they set up a fake timberwolf attack so Spike can save Applejack. Their ruse draws a pack of real timberwolves, which Applejack easily crushes, but the pieces form into a single giant beast and she gets caught in a rockslide. Spike throws a rock down its throat, causing it to choke and fall apart, and frees Applejack. The two decide not to worry about repaying favors done for each other in the future.
(More complete summary to come later)