Title says it all.
I have no idea, but I am forever scarred now. My image of the mighty lizard king will be tarnished forever by imagining him stalking prey with a goofy look on his face and walking like a pigeon.
With “Turkey in the straw” playing as the background music. 
I anticipate somebody posting the claim that they are a T. Rex, & claiming that they bob their head because “it feels good”.
I’ve been on this Board too long…
nods I think they did, or at least, that’s how I’ve pictured them moving. Mainly because of the whole fact that dinosaurs were more avian than reptilian.
I see them as having a slow up and down motion of their head when they walk, but no goofy look on his face.
Now did T. Rex hunt his own food or not, there’s a question…
. . . waits patiently for one of the biology heavyweights to analyze the situation . . . time’s up!
Bobs head like . . . say . . . a pigeon??
No way. A pigeon’s head weighs practically nothing, so moving it back and forth like crazy doesn’t take much energy.
Bobs head like . . . some other heavy animal: a giraffe? an elephant? a republican?
Lesse. On a Tyrannosaurus we’ve got a massive head at the end of a tilted neck. We’ve got two legs, and even if the thing wasn’t running, there’s be a big jolt when one of them came down.
T. Rex bobs head, yes. Answering Bosda, they did it, so it must have felt good. Or did I get that backwards?
We really know very little about the behavior of dinosaurs (despite what the Discovery Channel’s constant dino specials would have you believe). Just thinking about how the skull attaches to the neck and the overall posture of the animal, I believe a forward and back bob like a pigeon is unlikely, but there may have been a vertical bob when it walked. But being a predator, it may have held it’s head fairly still so as to stabilize it’s line of sight and more easily spot it’s prey.
So to summarize, I don’t know. 
This thread is better suited for General Questions. I’ll move it for you.
Cajun Man - SDMB Moderator
And more importantly, where are all the baby T-rexes?
So the thunder lizard diddy-bopped while hunting/looking for roadkill?
My god, T-Rex was the original Ganstah Pimp!
My favorite dinosaur as a kid is now wearing a goofy look, walking like a pigeon, shuffling his feet, and wearing a fur lined flop hat to the the soundtrack of Shaft.
Knowledge may be power but dammit let me hold on to a few childhood fantasies!
A thread moved from MPSIMS to General Questions? Is that a first?