The Bradys' dog, Tiger
The dog that played Tiger was hit by a car and killed early in the first season. When a replacement dog proved problematic, the producers decided the dog would only appear when essential to the plot. Tiger appeared in about half the episodes in the first season and about half a dozen episodes in the second season. The dog last appeared in "What Goes Up," which aired in 1971, and was not shown or mentioned again.
According to Barry Williams, the doghouse remained visible in the backyard set because it was used to cover holes in the artificial turf caused by a falling stage light.
In The Brady Bunch Movie, after Carol tells Mike "Go get 'em, tiger" she remarks to herself, "Tiger... Tiger... whatever happened to that dog?"
At the end of A Very Brady Sequel, a dog runs through the yard where a party is occurring. Cindy and Bobby turn to each other and say "Tiger?" Cousin Oliver chases the dog offscreen, which is followed by the sound of an unseen car crash. Cindy and Bobby seem unfazed.
The series pilot contained the only appearance of Fluffy, a cat that belonged to Carol's girls prior to her marriage to Mike. No explanation was given for the cat's absence in subsequent episodes.