@Perun I don’t know if Belarusians linked snakes to Veles. Veles is linked to underworld, while grass-snakes were worshipped.
Grass-snake worshipping was common to all Indo-Europeans in pre-Christian times. Because we remained pagan a bit longer despite being officially christian since 988 the cult of grass-snake survived in our part of the world longer. I don’t have any other explanation.
There is a legend about a zmej living in a stone that had windows and a door. Zmej was a skillful taylor and could speak people’s language. Zmej liked a girl. They lived together but did not have children. One day zmej asked the girl to look for clouds while he is sleeping. She should wake him when clouds arrive. She did awake him but he woke up hearing thunder. He slapped the girl on her face and she died. Zmej flew across the lake to his stone . Thunder struck zmej three times until he died. After that it was raining for 3 days. People buried zmej. On the next day zmej appeared on the surface. Perun struck dead zmej again and it was raining again. People continued burying zmej for several day and each time zmej was appearing on the surface it was raining. As a result everything was flooded around. Then an old man asked to gather all children and foals (baby horses) to bring sand to cover zmej. So they did. Since then there’s a Kurgan on that place.
That’s my bring interpretation of the legend. In details https://be.wikisource.org/wiki/Змееў_камень
Google translator works better when translating from one Slavic language to another than from Slavic to English.
Maybe there are other legend about zmej stone. I haven’t searched.