Wolf Bite can only target allied heroes. These are the error messages you get when targeting wrong things:

1. Targeting allied non-heroes: "Ability Can't Target Allies"
2. Targeting enemy heroes: "Ability Can't Target Heroes"
3. Targeting enemy non-heroes: "" (the red error message box appears, but it's tiny and empty)

It should be:

1. Ability Can't Target Creeps (dota_hud_error_cant_cast_on_creep)
2. Ability Can't Target Enemies (dota_hud_error_cant_cast_on_enemy)
3. Ability Can't Target Enemies (dota_hud_error_cant_cast_on_enemy)