During the "imagination" segment towards the end, the Spirit says to put a triangle in a perfect circle, and then turn the triangle. The image that results is a straight line that reaches both the top and bottom of the circle. There is no possible orientation that the original triangle could have to reproduce this visual effect in real life.
During the "billiards" segment, when Donald makes his first successful shot, the shadow of the actual billiards player who made the shot can clearly be seen on the table behind Donald.
Despite this being a mathematical education film, a character
incorrectly recites the value of the mathematical constant pi. The character states, "Pi is equal to 3.141,592,653,589,747, et cetera, et cetera, et cetera." The correct value of pi (to the same number of digits) is actually 3.141,592,653,589,793. (The last two digits are different.)