Clark is poisoned by a silver kryptonite splinter. When Clark is stabbed, the splinter is in his left index finger. Then, in the scene with Fine after class, (less than twenty minutes later,) Clark is seen rubbing his right index finger.
In the hospital, Lana has a large cut over her right eye. However, her head/face never struck anything, and when Clark is holding her in Lex's cellar, there is no cut on her face or head.
After Lana is warned by Chloe that Clark has gone all 'Captain Paranoid', she examines the silver 'meteor rock' more closely. We see a shot of her hand holding the 'meteor rock' but the hand that is shown is obviously not Kristin Kreuk's hand.
It is sometimes unclear which parts are Clark's illusions and which parts are real; however, as the scene continues normally after Clark leaves, the scene where Chloe subdues him with green kryptonite should be real, which leads to the question of how he could super speed away with little effort.