After the compartment where Willow had fainted in was cleared out, Casimir had promptly left the area and returned to his own room. He made some small talk with Artemis, bought a few things from the trolley, snacked, and then fell asleep. As far as he remembered, he slept for the remainder of the train ride, making the whole trip a quicker affair for him than usual. 
Casimir, along with everyone else who was on the train, arrived at Hogwarts a few hours later. He unboarded the train and greeted Hagrid out of respect before taking the boats to the mainland. Now it was time to take a ride on the carriages pulled by seemingly invisible horses.... except they weren't horses. Casimir couldn't see them, but he knew what they were. Thestrals. They were creatures that could only be seen unless one saw death, which up to this point, Casimir had seen none.... Thankfully...? The Slytherin also knew that many of the people who could see the invisible creatures only could because they witnessed the death of a family member, usually after said person died after experimenting with magic. Casimir would honestly be crushed if any one of his family died, as it would basically make him start losing the only people he really had in the world.

"Only a bit more waiting to do before we finally arrive at the actual school," Casimir said as he took an empty carriage for himself.