Within the bog, for the first time, Fenrir's excellent stealth abilities failed the duo. That was because as much as his abilities could hide them from being sensed, if the pup ran across a beast's nose, then it would not need to rely on spiritual sense to find them. The problem was that this example did not carry any exaggeration at all, and was exactly what the duo faced.
At times, the bog was so completely empty that they would not come across a single living thing. Other times, the place was so packed that let alone run from in front of a beast, Fenrir directly used a beast's head as a platform to jump over.
Yet what was fortunate was that none of the creatures chasing them held any considerable threat. In fact, the reason they were chasing was because Lex and Fenrir couldn't be bothered to deal with them, as it would be too tedious. Besides, after chasing them for a while, the beasts would either get tired, or return to their respective territories.