Revealing mistake: Whilst imprisoned by the Burpers, Brother Belcher calls to one of the guards. The guard's supposed to have many missing teeth, but they have just been very obviously blacked to simulate this (a very common film or theatre trick, but usually not this obvious).
Revealing mistake: Look at the table when the fakir's "severed" head is revealed during dinner at the end. It noticeably wobbles and moves about when he talks, showing his body is hidden underneath.