During the episode, Martin becomes convinced the Leland (played by David Ogden Stiers) is the real father of Frasier and Niles due to their shared interests and unlucky timing of Martin walking in on Leland with Frasier and then Niles doing fatherly stuff (reading a story to a sick Frasier in bed and then helping Niles walk off a stiff leg). When Martin finally asks Leland about it at the end of the episode, Leland reveals his homosexuality. David Ogden Stiers has since come out as gay.
When Leland Barton (who worked closely with Martin's wife) arrives to visit Frasier and his family, Martin has some doubts if he really is the father of Frasier and Niles, since Leland shares so many interests with Frasier and Niles. In Cheers, Frasier stated his father was a research scientist. It is then referred to in the episode "The Show Where Sam Shows Up" and explained the discrepancy.
Niles: Leland, it is such a pleasure to talk shop with a fellow nutcracker.
Leland: And talking to you Jung people makes me feel like an id again.
Niles: Do you have a pun, Frasier?
Frasier didn't, but he might have responded, "I'm a-Freud I can't think of one".
Frasier: (hearing of Daphne's and Niles' childcare application) Do I hear the pitter-patter of petite elite feet?
Niles: How 'bout Desmond?
Daphne: Desmond Crane. 'Desmond Crane, you are hereby sentenced to...' No. I don't like it.
Niles: (responding to one of Daphne's name suggestions) Now you're just reading from the spice rack.
Frasier: When I can't give an opinion, you may as well call the coroner, tag my toe, I'm dead.
Martin: By your logic, everyone on the cooking channel's their father.
Hogan's Heroes: When Niles has Daphne pick a first name out of the phone book, the name she chooses is Bob. Bob Crane portrayed Col. Robert Hogan in the 60's TV series Hogan's Heroes, but was more well known for the bizarre lifestyle he led following the show.
The Legend of Sleepy Hollow: The name Roz picks for the application is Ichabod Crane. Ichabod Crane is the protagonist in Washington Irwing's "the Legend of Sleepy Hollow", which was filmed by Tim Burton in 1999 with Johnny Depp playing Ichabod.