My silverfish spawner shows a pig inside of it

When i wanted to go to the end my silverfishspawner doesn't light up only when i klick on the spawner and then there was a pig inside it.

i thought there would spawn pigs but i put grass there and it didn't spawn pigs.

Steps to Reproduce:
i don't know how to Reproduce it. I just suggest to go to the end portel.

i dont know how to make a world download i'm sorry.