Item sharing

As a rule, Items in Dota 2 cannot be shared with other heroes. The purchasing Hero is considered the owner of the item and only he can use, sell, or upgrade it. However, since Consumables cannot be upgraded into other items and only grant temporary effects, they can be freely shared (used or sold) with all other heroes. This is important, since it means that support heroes can purchase Sentry Wards or other Consumables on a courier and other heroes can place them.

Other, permanent but low level items that grant regenerative abilities are considered partially shareable. This means that other heroes can pick them up and benefit from the effect of the item, but cannot sell or upgrade the item. Divine Rapier is also partially shareable because of it's unique mechanic.

Finally, certain items have disabled abilities when placed on the Animal Courier, to prevent abuse.

Partially Shareable Items
Note that unlike the original DotA, Bottles filled with Runes are not shareable (see August 5, 2011 Patch Notes). However, partially filled bottles are still partially shareable.

Completely unsharable items

 * All recipes
 * Everything that requires a recipe except Flying Courier
 * Everything else not noted above.

Disabled Items on Courier

 * Helm of the Dominator due to Dominate ability
 * Armlet due to Unholy Strength
 * Shiva's Guard due to Arctic Blast
 * Gem of True Sight due to True Sight

Note that Flying Couriers are also unable to pickup the Aegis of the Immortal.