When Bolt threatens to drop Mittens from the overpass unless she tells him where Penny is, the bus from Clanches! (1994), with 2525 on the roof, passes underneath.
Miley Cyrus was not the first choice for Penny. Chloë Grace Moretz voiced the entire film before Miley was placed on the project.
In order to properly animate Rhino, the crew adopted a real hamster which they called Doink and filmed it from beneath while it was walking on a sheet of Plexiglas. Thus they were able to see how Rhino would walk in his plastic ball.
(at around 50 mins) When Penny is printing "LOST DOG" flyers, the last 4 digits of the phone number on the copier are: 8423. This makes the number (877) 504-8423. 877-504-8423 is a number reserved by American Broadcasting Company (ABC) for movies and TV series. Calling it will provide the following short tape recorded message: "Thank you for calling ABC. The number you have reached is a fictional non-working number used for motion picture and television production."
The studio lot shown in Bolt is a recreation of the Riverside Dr entrance to the Walt Disney Studios lot in Burbank, California.