He regurgitates the slimy creatures for ages after his spell on Malfoy backfires.
'Taste really nice'
Rupert Grint, who plays Ron, said the slugs were his favourite scene. "That was so fun because they had all these different flavours of slug slime," he told Newsround's Lizo Mzimba.
"There was chocolate, there was lemon, there was orange, there was peppermint. All these different flavours - they made them taste really nice."
But at least one child in every screening is sick during that scene, said Gudrun Romsbotn, who manages a cinema in Stavanger, Norway.
"If the children have eaten popcorn or sweets when this scene is shown, they feel sick," he told a Norwegian newspaper.
"It is not a particularly fun task for our employees to have to wash away the sick."
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Rupert Grint: our full interview
Did you puke during Potter?
