Celia is normally a kind sweetheart, especially to her boyfriend Mike. While she may have an explosive temper when angered, she can calm down almost immediately when she is told the truth by Mike.
The snakes that make up her hair have a mind of their own; they make chirping noises when they're happy, rattle and hiss when they're mad, and they express fear when Celia thinks about getting a haircut (to which Mike respectfully objects, thus relieving them).
While absent from the film, a picture of Celia is seen along with her phone number in Mike's locker towards the end of the film.
In the first film, Celia is celebrating her birthday, so Mike invites her to a Japanese restaurant called Harryhausen's (named in honor of legendary stop motion animator Ray Harryhausen), but due to Boo being in the restaurant, the place is decontaminated by the CDA. One device that is made to make a large dome that would get rid of fatal germs, but could harm people without CDA armor, which is why Celia comes back to work the next day with serious injuries. She is initially upset with Mike and complains about how the date was ruined, but when she sees Mike in danger of being captured by Randall for devious purposes, and when Mike reassures his love for her, she saves Mike by subduing Randall with a crowd after she feign-announces him breaking the all-time scare record. She is seen again at the end of the film, having fully recovered and made amends with Mike, and tells him that a box full of magazines has just arrived. Both she and Mike are surprised to see that Mike has made the cover of the magazine. She kisses him and her hair tickles his face.
The year before the film takes place, she and Mike are supposed to have won the 7-legged race at the year's company picnic.
She also appears in the company play "Put That Thing Back Where It Came From Or So Help Me" that stars her boyfriend, who has also written, directed, and produced the play.
Celia makes a very minor appearence in the ride. Her voice is heard over the intercom telling the guests when they can enter the laugh floor.
- Celia's name may be a play on the word "Cecaelia." It might also refer to Scylla, a monster in Greek mythology known for snatching up those who strayed too close to her with mouths attached to tentacle-like limbs (somewhat like Celia's snakes).
- According to the book Monsters Inc.: The Essential Guide, the five snakes serving as Celia's "hair" are named Amelia, Bobelia, Ophelia, Cordelia and Madge.
- Celia makes a cameo in M.U. on a picture in the ending. Her phone number can also be seen.
- It's implied that Mike may have met Celia sometime after getting a job at Monsters Inc.
- Celia's age, according to the handbook, is probably 24, making her a few years younger than Mike.
- Celia having snake for hair may have been a nod to the Greek mythology legendary figure, Medusa. Unlike Medusa who is bitter and can turn people into stone however, Celia is kind and does not have any abilities.
- The read along version never shows any of the scenes in which Mike wins Celia back. This could fool the reader into thinking that Celia didn't appear again.