Hamlet Soliloquy Glossary: O, what a rogue and peasant slave am I! (2.2.555-612)
monstrous that this player...For Hecuba! (556-63)
This passage is often very difficult for students, and standard annotations leave them wanting. So it is best paraphrased:
Is it not horribly unfair that this actor, pretending to feel great passion, could, based on what he has conceived in his own mind, force his own soul to believe the part that he is playing, so much so that all the powers of his body adapt themselves to suit his acting needs -- so that he grows agitated ("distraction in's aspect"), weeps, and turns pale ("wann'd")? And why does he carry on so? Why does he pretend until he truly makes himself weep? For Hecuba! But why? What are they to each other?