Continuity mistake: When the princess and her chambermaid are talking about William and how they killed his wife, at the end of the conversation, the princess leans back against the edge of the archway. In the next shot from over her left shoulder, she's not leaning back, but sitting straight up.
Continuity mistake: After being knighted, William says that he will invade England. In the close-up shots of Robert in the group reacting to him saying this, you can see the man whose bride was taken away by the English lord earlier in the film behind him. But, in the wide shots, he's not there. It's just some random man behind him.
Continuity mistake: After Wallace kills the noble and his crew for killing his wife there's blood on his face. At the funeral there is no blood on his face. The night of the funeral the blood on his face returns.
Answer: It's called "A Gift of a Thistle" and it's on the soundtrack conducted by James Horner. Incidentally, the tune is a recurring theme throughout the film's music, and appears in several other songs on the soundtrack as well. Also in relation to the song, the flower was a thistle.
Krista