We've reached an era of special effects where almost anything can be done in a computer, but that doesn't mean it can all be done well. Brothers Colin and Greg Strause know this better than anyone: The two of them have logged over fifteen years in the effects industry, and they and their company Hydraulx have worked on concocting CG visuals for films like Titanic, 300, The Day After Tomorrow, and Avatar. The brothers' new film is Skyline, which they also directed, and it represents one of their greatest effects challenges yet: an elaborate alien-invasion movie, brought in for under $20 million (in fact, physical production for the film only cost the brothers $500,000, and they spent the rest of the budget on large-scale effects). Who better, then, to fill Vulture in on the four types of special effects that are still really, really hard to do?

Fur
W.C. Fields famously recommended never to work with children or animals, and when it comes to the latter, special-effects artists can attest to the hassle. "Computationally, fur is so intense that it slows everything down so much," groans Colin. "This is a highly iterative process, so if it starts taking days and weeks to see results instead of minutes and hours, that really can crimp the process." The problem, Greg says, is in the sheer amount of separate items that need to be animated for simulated fur to look convincing: "If you're doing something like a dog or a wolf or some sort of creature, you're really talking about hundreds of millions of hairs and how they move and clump together and collide with each other. And long fur! [Peter Jackson's] King Kong is still some of the best long fur I've seen in a movie, but longer fur is still really hard to do."

Dust
"Big volumetric stuff like dust clouds — we did a lot of that in Skyline — there's still a lot of challenges," says Colin. "It's getting easier, but it's still difficult." In fact, the brothers say the technology for the effect has come a long way in the eighteen months since they animated dust clouds to accompany the collapsing Three Mile Island in X-Men Origins: Wolverine. Now that they've boosted the RAM in their computers from 16 to 64 gigabytes, "just having that huge amount of RAM is enabling much bigger volumetric effects to be done," says Greg. "In Skyline, we had huge dust effects as the aliens were sucking everyone into the air, and half of that was done with some proprietary tools that are integrated into an off-the-shelf package, and then the other effects were just done with an off-the-shelf package and artists really pounding on it."

Water
"We've done a lot of water stuff over the last year and it's still challenging," says Greg. "I think the issue is that the bar keeps getting raised as to how real everything needs to be. Audience expectations continue to go up and up." Still, the brothers stress how far water effects have come since they worked on 1997's Titanic: "One of the reasons is that processing power is so much quicker now, so many orders of magnitude faster," Greg says. "It makes the ability to do highly detailed, fluid simulations easier. You can see results now in days when it would have taken months or years back when we were doing Titanic." Oddly enough, the brothers credit the high need for fire and explosion effects with hastening the ability to simulate water. "A lot of the same software that they use to do water and other volumetric effects, you just color it differently and it's fire," says Greg.

Breath
The Strause brothers are very proud of the facial-mapping work they did on The Social Network to convincingly split Armie Hammer into two Winklevoss twins, "but we did not do the breath, if that's where you were going!" laughs Greg, referring to the film's most debated special effect. "We did very nice breath on Benjamin Button and [David] Fincher's Nike commercial, but did not do it on Social Network." Says Colin: "We're good friends of David and big fans, and we would never be portrayed as anything but. However, I have read reviews [that pointed it out] and we have had people asking if we did the breath ... I think they had a bid on it and maybe they didn't have enough money — I'm not sure what the issue was — and some other vendor did it." Is breath still a difficult special effect for most effects houses to pull off? The brothers think they can nail it, though they admit, "It's a lot easier to do now than when we did it in Titanic. They were shooting photographic elements for breath back then, and now we just synthesize all of it."