Filming for Episode 4 continued today, with our first proper glimpse at one of the new monsters being introduced in series 8, who seems to have wandered straight off the set of a Guillermo Del Toro flick. It's also more than likely the mysterious monster who was given the goofy cow-shaped silhouette at this year's London Toy Fair, though as you can see from the photos below, it's more eye-stalky than bovine in appearance.
These are all slightly enlarged images from mugim0e's Flickr page and he has several more photos of today's filming including the Danny Pink character wearing one of the Sanctuary Base style orange space suits outside the TARDIS, and some green screen filming involving The Doctor up an alien tree with a set of binoculars.
There was also some night shooting involving Jenna stumbling around a spooky forest terrified and sneaking around a giant tree trunk.
We also have reports that the Danny Pink character has been aged between scenes, and during Clara's forest sequence someone was reading in two different takes of some voiceover dialogue (presumably Clara's to be added in post): "When you talk to yourself...what if it isn't you you're talking to?" and "When you talk to yourself... what if the person you're talking to isn't really you?"