When travelling to or from Denmark, you pay a Child ticket for larger pets, while smaller ones in a cage travel free of charge.
The Animals Allowed section is placed in car 13 (and, when applicable, in cars 23 and 33). Service dogs are allowed free of charge in the entire train in both Sweden and Denmark.
It is possible, but not mandatory, to reserve seats in the Animals Allowed section. There is a total of 20 seats, whereof four can be reserved. When purchasing a ticket, select "Djur tillåtet" (Animals Allowed).