A deer from Montana is subject to these requirements:
https://apps.leg.wa.gov/wac/default.aspx?cite=220-413-030"Soft tissue" would include the brain and eyes. The cape must be detached from the head.
Importation and retention of dead nonresident wildlife.
(1) It is unlawful:
(a) To import or possess dead wildlife, taken in another state or country, into Washington unless such wildlife was acquired lawfully. Proof of legal acquisition must be retained during the period of retention of the carcass or edible parts.
(b) For a person who imports a dead bighorn sheep, mountain goat, cougar or bear to fail to report such importation to the department in writing within ten days of the importation. The report must contain the name and address of the importer, the location where the dead wildlife is being stored, and general information describing where and how the wildlife was obtained.
(c) To import or possess deer, elk, or moose, or parts thereof, harvested in Pennsylvania, Texas, Missouri, Colorado, Wyoming, Utah, New Mexico, Wisconsin, Illinois, South Dakota, Nebraska, Kansas, New York, West Virginia, Virginia, North Dakota, Alberta, Maryland, Minnesota, Montana, Mississippi, Iowa, Arkansas, Michigan, Saskatchewan, and Tennessee with the following exceptions:
(i) Meat that has been deboned in the state or province where it was harvested and is imported as boned-out meat;
(ii) Skulls and antlers, antlers attached to the skull plate, or upper canine teeth (buglers, whistlers, ivories) from which all soft tissue has been removed;
(iii) Hides or capes without heads attached;
(iv) Tissue imported for use by a diagnostic or research laboratory; and
(v) Finished taxidermy mounts.
(2) Violation of subsection (1) of this section is punishable under RCW 77.15.290 Unlawful transportation of fish or wildlife—Penalty.
(3) It is unlawful for an importer or receiver of deer or elk to fail to notify the department within twenty-four hours if a state or province alerts the importer or receiver that a harvested animal has tested positive for chronic wasting disease. Violation of this subsection is an infraction punishable under RCW 77.15.160 Infractions.