What happens toward the end of the first book of Maus that gives name to the chapter “The Mousetrap”?

The closing chapter of the graphic novel Maus I is entitled "The Mouse Trap" because it is metaphorically referring to the deception of characters Vladek and Anja that leads to their imprisonment in the Auschwitz concentration camp. The metaphor of the mousetrap plays on author Art Spiegelman's casting of his Jewish characters as mice within the narrative. 

In Maus I, the reader is introduced to the main character of Art, who is trying to come to terms with his relationship with both of his parents through an understanding of their early years as persecuted Jews in Nazi-controlled Europe. Over the course of the book the reader travels along with Art on his visits to his father, Vladek, and through each encounter the reader learns more of the story of Vladek and Anja (his wife, Art's mother) and their attempts to at first ignore and later escape persecution by Nazi forces. 

The sixth and final chapter of the first book is the culmination of these attempts to escape, as within it Vladek reveals just how desperate they were becoming to avoid deportation to a concentration camp. In the closing pages, Vladek has arranged for the couple to escape by paying several seedy characters for tickets out of the country. Shortly after their train departs, though, its cars are stormed by the Gestapo, and Vladek, Anja, and all other Jewish peoples on the train are rounded up and sent to Auschwitz.