Small chest
From CC Wiki

Small chests are objects, originally from Celeste Classic, that spawn a berry when a key is collected. during the spawning animation, the chest shakes randomly, which causes the berry to spawn at a random x position.
original code
chest={
tile=20,
if_not_fruit=true,
init=function(this)
this.x-=4
this.start=this.x
this.timer=20
end,
update=function(this)
if has_key then
this.timer-=1
this.x=this.start-1+rnd(3)
if this.timer<=0 then
sfx_timer=20
sfx(16)
init_object(fruit,this.x,this.y-4)
destroy_object(this)
end
end
end
}
Unused sprite

In Celeste Classic, when a chest spawns a berry, the chest simply disappears. However, in the game's spritesheet there is a sprite that was likely supposed to depict an open chest. This is one of the few unused sprites in the game.