RE: Lost one.
A gut shot deer will stop for 5 minutes if no vitals are hit,Unfortunately in my early years I have seen this happen.BUT there will usually be a puddle of blood where he stopped.
The thud was either the guts exploding or you hit a tree.Go back and check to see if the arrow is stuck in a tree,even look up in a tree,you never know if you hit a limb and it deflected at the last second.