The head of wardrobe will have her hands full throughout the production.
The famous story of the revenge-seeking London barber hits the Vancouver opera stage on Saturday night. With all the throat-slitting and production gore that comes with the show, it can seem like a nightmare for the wardrobe team.
"It's a particularly ugly mixture," she said of the fake blood used during the show. "Because a lot of it is around the actors' mouths, it has to be edible."
Underhill says the mixture is made up of chocolate sauce, corn syrup, and red food colouring. While convincing, the fake blood can be difficult to work with as it also needs to be taken off the costumes immediately.
Underhill and the rest of her dressing team operate feverishly backstage with only limited lighting. She says they often need to use flashlights in their mouths or headlamps when making last minute repairs to costumes.
Underhill says time is of the essence in this type of production.
"It's extremely busy. Some of the changes are as short as 30 seconds."
Despite the frenzy, she admits the work is worth it in the end.
"Once the show's in the theatre, it's kind of my baby. It's up to me to deal with the problems and make sure everything is ready for every show."
"With a big complicated show like this, there is a great deal of satisfaction when it does all come together."
Sweeney Todd: The Demon Barber of Fleet Street runs until May 3rd, 2015 at the Queen Elizabeth Theatre.
To hear the full interview with Sheryl MacKay, click the audio labelled: Backstage with Sweeney Todd's head of wardrobe.