Complex sentence: After running off with the little pup, moments later, Tom realizes his mistake, turns around to see a sleeping Spike feeling for Tyke and rushes back into Tyke's place, taking on the role of Tyke so Spike doesn't know that he took Tyke.
Split into simpler sentences: After running off with the little pup, moments later, Tom realizes his mistake. Tom rushes back into Tyke's place, taking on the role of Tyke so Spike doesn't know that he took Tyke.