While putting your favorite condiment on a sandwich, you accidentally make a magical occult symbol and summon a demon.
You silently take two more slices of bread out of the package and make another sandwich. You put it on a plate with a handful of potato chips and hand it to the demon. He takes the sandwich, smiles and vanishes in a puff of demonic smoke.
The next day you get that job promotion you were after. There was no contract.
No words spoken. You owe nothing. But every now and then, another demon pops in for lunch. Demons don't often get homemade sandwiches.