After the big shootout where the Predator gets wounded, his blood is on the leaves. Yet, not even Billy saw the big, flourescent green thing shining. "No blood, no bodies, we hit nothing" but it's right in front of them. Anna saw it, so how the hell did the team miss it?
On a side note, right after that, Dutch orders Mac to set up claymores around, knowing well he was close to Blain. A bit of dick move from Dutch? Show a little compassion, have someone else place the mines. He even has him do the first watch. Scumbag Dutch.