After verbs like throw, jump, push, put, fall, we can use both in and into, or on and onto, to indicate directional movement. We use into or onto when we think of the movement itself, and in or on when we think more of the end of the movement – the place where an object or person will be.
He fell into the mud.
Put the cheese in the fridge.
She threw her jacket onto the sofa and turned the TV on.
Throw in some more sticks on the fire.