Hedgehog in the Fog (Russian: Ёжик в тума́не, Yozhik v tumane) is a 1975 Soviet animated film directed by Yuriy Norshteyn, produced by the Soyuzmultfilm studio in Moscow. The script (in Russian) was written by Sergei Grigoryevich Kozlov, who also published a book under the same name.
This is a story about a little hedgehog (voiced by Mariya Vinogradova) and his friend bear cub (voiced by Vyacheslav Nevinniy). They would meet every evening to drink tea, converse, and count the stars. One day, the hedgehog decided to bring raspberry marmalade. As he went to the bear to count the stars, he passed through the woods and found a horse standing in a fog. He is curious as to whether the horse would suffocate if it lay down in the fog. Being an explorer, the hedgehog decides to explore the fog.
Hedgehog in the Fog has a fanclub.
If you're interested, this is a history of Russian animation.