When Shaggy says, "I thought that rock looked pretty suspicious.", his hair is blonde.
As Velma is identifying the glowing seaweed from the biology book, the title of the book is located on the back of the book.
At the restaurant when the kids are reading the newspaper, Scooby puts straws together to steal from Shaggy's drink, and succeeds until Shaggy cuts the straw. After Velma says, "That solves the mystery!", the focus is on four drinks on the table, and they are all full. Shaggy never got a refill.