When Thorne is talking to Sol in the "suicide facility", at one point the inter-phone starts malfunctioning and the "speaking permitted" light starts to blink.
If you look at the cable coming out from the lower-left corner of the device, you'll notice that they are obviously alternating two still frames to achieve the blinking effect, as it jumps erratically from one position to another.
When Thorn is running to the euthanasia building to try and stop Sol, he is limping from just having been shot in the leg. He gets there too late, so he follows Sol's body as it is disposed of. He goes through a long sequence in which he is repeatedly required to dart, scurry and jump, which he accomplishes with nimbleness and no sign of the leg injury. Later, as he is fleeing gunmen in the running shootout, he is limping again.
When Thorn is in the Soylent Green factory, he knocks two factory employees off the catwalk. A stunt mattress can clearly be seen sticking out from underneath the conveyor belt where the second one lands.
When Thorn is running towards the "going home" building, his head disappears into the matte just before the shot cuts. Later in the same scene, as he sees Sol "going home", part of his arm disappears behind the orange wall seen through the window.