What "cold trailing" means in forest fires

"Cold trailing is when firefighters form a line and walk the area, feeling with their hands for heat coming up out of the ground and looking for signs of continued burning that could be underground."

http://www.castanet.net/news/Kelowna/146840/Fires-100-contained

I'm sure this is a very tedious part of firefighting. Here's some rather bland footage of the painstaking work.