Minecraft slime spawning?

How can you spawn Minecraft slime on a player without it being chatting that they spawned?

In the sense of (for stupid -so for me)

you want to produce something without the penny appears?

Kurtz… Make invisible and let yourself spawn

I'll bet you want somebody to troll

In order to get no feedback from commands, you first have to write this here:

/ gamerule sendcommandfeedback false

If you did that, you'll get another message: "gamerule sendcommandfeedback was set to false"

Then you get, no matter which command no issue in the chat.

If you want to turn it back on you have to write this here:

/ gamerule sendcommandfeedback true