What's missing from this picture revealed

You guys sent in some great suggestions for this one, which I've held off on posting until now so as not to spoil the fun for those who came after. There were several variations on the idea of "tugless towbars"; I think someone also mentioned "stealth" tugs.

I wasn't working ground control at the time this occurred, so I'm not sure what lead up to the initial shot I showed you. Shortly after, a tug arrived on the scene, as shown here. As B757s generally taxi right onto this gate (73), there must have been some sort of interesting scenario. One is that the aircraft was being towed up to the gate from the maintenance ramp when something happened to the original tug. Another possibility is that it was an inbound flight that experienced some sort of steering issue as it approached the gate. Or perhaps there was just a miscommunication between the cockpit and the ground crew. A tongue-in-cheek alternative (I hope) is that they ran out of fuel just as they were about to pull on to the gate; I've heard of that happening, although I've never personally witnessed it. I have personally worked aircraft being towed when the tug ran out of fuel, and that was bad enough (would someone please call AAA?!?) Stick around; we're gonna do it again!