Kat (Mayim Bialik), shows the group her orthopedic shoes. Mayim's character, Amy Farrah Fowler in The Big Bang Theory, also wore orthopedic shoes.
Mindy shows Kat (Mayim Bialik) a picture of her son who "has so many trains they might do a Youtube about him." Mayim's character, Amy Farrah Fowler in The Big Bang Theory, is dating/married to Sheldon, who is not only obsessed with trains but has his own Youtube show (not about trains).