In the beginning of the episode (at 1 minute 30 seconds), Dawn says "The game is afoot" which is one of the signature sayings of Sherlock Holmes, the famous, fictional "consulting detective" created by Sir Arthur Conan Doyle in 1887.
Immediately after the Sherlock Holmes quote, Dawn also says "Project Parent Trap begins now!" Parent Trap was a 1961 Disney film starring Haley Mills playing two roles as twin sisters who conspire to get their divorced parents back together again. A remake was released by Disney in 1998 starring Lindsay Lohan in the dual role of the twin sisters.