"When I pet my cat near her tail, it immediately shoots up." Although it's been jokingly referred to as a "tail erection," the reason cats do this is that when they were kittens and their mothers cleaned them, they raised their tails so she could "inspect" the area. (Incidentally, if your cat puts her tail or bottom near your face, it means she's accepting you as the dominant person in the relationship.)
"My male cats mount each other." This is not uncommon, especially if there are no female cats around. Yes, they could be displaying sexual interest. But mounting between any sexes can also be a of dominance, or sometimes even just plain old boredom. (The same is probably true for people, too!)
"My cat sneers when he sees an opposite sex cat." That look of contempt is actually "flehming." The cat takes an odor and intensifies it by sending it up to another sense organ in his head. Almost all male cats "flehm" when they investigate the genitals of a female cat, and some female cats do it also.
"When my male cat sees a female one, his jaws start chattering." Cats sometimes do this in anticipation of something delicious. Like when they see potential prey, such as a bird. So it could be a sign of a hunger other than sexual."
From 277 Secrets Your Cat Wants You to Know by Paulette Cooper and Paul Noble.