Memory
The memories hit him hard.
The crack! of a belt, the harsh bellows of a fat, terrifying giant, the high shrieks of a skeleton, the painpainpainpainpain and the cold, squeezing sensation, he couldn't get out! – 'Let me out, please! Uncle, please! I can't breath-'
And then he is enveloped by warmth. The comforting arms around him slow his frantic heart and she's whispering, 'It's just a boggart, Harry. It can't hurt you, I promise. It's just a memory."
And then he opens his eyes.