From Bulbapedia, the community-driven Pokémon encyclopedia.
In Galar, Slowpoke gains yellow markings on its forehead and tail. This was a result of eating Galarica seeds which were their favorite food. As a result, Galarian Slowpoke built up particles of the spice in their bodies over several generations.
Galarian Slowpoke spend their their days wallowing on seashores and riverbanks without thinking about anything in particular. Once in a while they might get a very sharp look in their eyes, but they will soon revert back to their zoned-out expression. It’s thought that this behavior is caused by the accumulated Galarica particles stimulating Galarian Slowpoke’s brain, resulting in it thinking of something tremendous—only for the Galarian Slowpoke to immediately forget what it had just thought of.
==In the anime==