Poor Pikachu. The character shows up for a Pokémon "quiz rally", and a bunch of Japanese kids stuff their fists into his mouth. The nerve!
The official (and current) Pikachu costume worn at events features the character with an open mouth, presumably so the wearer can see out and not so children can stuff their little hands in his piehole.
ポケモンクイズラリー参加してきたｗピカチュウがやばいことなってたｗｗｗｗｗ [Twitter]