当我使用pygame.sprite.spritecollide()时，为什么只有项目符号消失了？

import pygame
from pygame.sprite import Sprite, Group

# 创建精灵类
class Block(Sprite):
    def __init__(self, x, y):
        super().__init__()
        self.image = pygame.Surface((50, 50))
        self.image.fill((255, 0, 0))
        self.rect = self.image.get_rect()
        self.rect.x = x
        self.rect.y = y

# 初始化pygame
pygame.init()

# 创建屏幕
screen = pygame.display.set_mode((800, 600))

# 创建精灵组
blocks = Group()

# 创建精灵对象并添加到精灵组
block1 = Block(100, 100)
block2 = Block(200, 200)
blocks.add(block1, block2)

# 游戏主循环
running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    # 碰撞检测
    collisions = pygame.sprite.spritecollide(block1, blocks, True)
    for collision in collisions:
        # 处理碰撞的结果
        # 例如，移除碰撞的精灵
        blocks.remove(collision)

    # 绘制精灵
    screen.fill((255, 255, 255))
    blocks.draw(screen)
    pygame.display.flip()

# 退出游戏
pygame.quit()