When Dr. Cuddy walks in to ask House about the patient's boob job she is wearing white heels, in the next shot she's wearing black heels.
When House asks Amber for his car keys back he says "and no more prime numbers for you." You can't actually see her number in this shot, but Amber's number is 24, not a prime number.
In the hyperbaric chamber, the sprinklers go off after the fire is out.
House could not hire the applicants and merely divide the 3 salaries among them, because much of the cost of the employees would be their benefits (health insurance, etc.) as well as the employer-paid taxes such as Social Security (the employee pays half and the employer pays half). Each employee would also bring the burden of the employer paid unemployment insurance.
Dr House has all the applicants in the classroom wearing numbered ID tags. When he calls out numbers to allow them to ask questions the numbers he calls do not match the numbers worn by those who respond.