Know how if you hit spikes in Sonic 1, you bounce backward because it registers as a hit, and then if you fall on spikes again, you instantly die? Well that's what has been used to show that here. The same spot in Green Hill has been used to demonstrate the problem. Sonic jumps into the right set of spikes from the left, and then he bounces backward and falls on the left set. In the top two pics, the spindash
option has been turned OFF. The game plays like normal, if you hit spikes while you're flashing, you die instantly. (Included are two shots of each, one with the pause menu, and one with it cleared by pressing X+Y+Z, to show that they aren't doctored pics)
But in the bottom two (with spindash ON), Sonic got hurt and bounces back, but he just stopped and stood on the spikes.