When Peter first climbs up the wall, if you look closely enough you can see Peter's shirt is hanging towards the wall, which indicates that it isn't really a wall he is climbing. It is the floor turned vertically.
Well come on, an actor can't actually climb up steep walls. The effect of him climbing up the wall, with out computer generated effects, was done cheaply and effectively. You can hardly notice it.
Well come on. The scene was done effectively with out computer generated effects. And the shirt wasn’t hanging by that much, and inch at most. That isn’t so bad.
i would like to point out the lighting though. when the shot changes from a medium side shot of peter to a medium-close shot of him crawling towards the camera. the lighting on the wall is different. also the light source for the scene is supposed to be the sunlight/sky. why then is peter's shadow perfectly cast as if the light was coming from behind his back. hmm thats all...