Harry gets a cut on the back of his hand at some point when he’s tearing up the house (you don’t actually see him get cut, just the aftermath) and the Henderson’s treat the wound
When a pool cleaner scoops a bunch of Harry’s hair from a woman’s pool, he says “you don’t have a cat, do you?” implying that the giant clump of hair could be a dead cat. She says no, and he says “good, so it’s just a hairball”
No, but the Henderson’s nosy neighbor goes through their fridge at one point looking for foods she can eat on her new fad diet. It’s implied that the dieting is standard behavior for her and she’s seen exercising at least once later in the movie