The snake on Harry's belly is a black & white grass snake for most shots, but in one shot he lifts the bed sheet and the snake is, instead, a brown boa constrictor.
Saeed Jaffrey (as Dr. Kunzru) stated that the Krait is one of the most poisonous snakes in the world. What he should have said was one of the most venomous, not poisonous.
Should really be titled Venom as a Krait is a venomous snake, not a poisonous snake. The short story by Roald Dahl on which this adaptation is based is also incorrectly titled 'Poison'.