Walden was a male cat, and males of the feline persuasion are known by a particular characteristic.
Veterinarians will tell you that male cats that are not neutered will continue to engage in marking activity even after they have been spayed. It's a sort of an instinctive action that does not turn off once it has been turned on.
Walden was also a curious cat. Curiosity will get a cat into all kinds of trouble...
Nitrous oxide was a hot commodity in our dorm; it was usually dispensed in little canisters called Whippets which were used to discharge whipped cream on top of ice cream sundaes. It could also be procured in balloon quantities. It livened up many a party; people who inhaled it would fall down laughing (or just plain fall down). Helium, by contrast, just made you talk funny.
I've owned many cats in my life. I've only owned one dog, and he tends to drive my current cat nuts.