In the homecoming game scene, the twins trounce the Nantucket Whalers while playing for the Martha's Vineyard Vineyarders. There is a very close rivalry between both high school football teams and many people from Martha's Vineyard were delighted to see the Whalers lose on film. Nantucket had no comment.
On the way to the hospital, when Morty pulls up next to the moving car in his scooter, he is holding a cigar in his hand; the smoke is blowing forward, not backward as it should on a moving vehicle.
While it's true that in real life Bob and Walt cannot possibly be conjoined twins because they are not identical, this movie is a comedy and the filmmakers obviously chose two actors who look nothing alike as a joke. The plot also gives a pseudo-scientific explanation involving their liver for why they look different.