Continuity mistake: When Ted is using the kite to steer the balloons, he is holding the string in his hand. When George's balloons pop, Ted catches George, and both of Ted's hands are seen to remain empty for at least 15 seconds, no kite or string is seen at all. Then it immediately cuts to a wide shot after George climbs onto Ted's back, and Ted is suddenly holding the kite string, and we see him continue to use the kite to steer the balloons. Ted did not have time to tie the kite string anywhere else, as he had it in his hand as he reached for George.
Continuity mistake: George puts one of his feet in the can of red paint and then walks to the bathroom. He leaves footprints on the floor with one foot only. When Ted arrives at the apartment, he sees George's footprints leading to the bathroom and there are red footprints for both feet.