 Fluid breathing is a reality. Five rats were used for five different  takes, all of whom survived and were given shots by a vet. The rat  that actually appeared in the film died of natural causes a few  weeks before the film opened. According to James Cameron (I) (qv),  the scene with the rat had to be edited out of the UK movie version  because "the Royal Veterinarian felt that it was painful for the  rat". James Cameron (I) (qv) repeatedly assures that the rats used  for this take didnt suffer any harm.