In many episodes the surgeons are incorrectly wearing their stethoscope. The ear pieces should face away from you when donning the stethoscope in order to have better placement in the ear canal.
In the NICU, when George starts boasting that he has the best quint, in the overhead wide-shot the T-mark (greenish-yellow) is visible on the floor near Kate, moments before Karev walks in and stands there. It's visible again just as Karev walks away.
When Burke hands Cristina the cup of coffee as she leaves for the hospital, blue screens can be seen in his eyeglasses.