During a key moment in Sunday's episode of The Walking Dead, the AMC series chose to focus on tiny but potentially important detail.
Spoilers for The Walking Dead Episode 8x04, Some Guy, follow.
Following King Ezekiel's freedom from captivity, the leader of the Kingdom fled through the woods alongside Carol and Jerry. Along the way, however, the trio encountered a herd of walkers which would have been too much for them to handle in their beaten conditions. Shiva pounced to their rescue, ultimately sacrificing herself, and realizing a fate true to the comics.
As Shiva's blood flowed through the river, however, there may have been an important detail which came into the frame's focus. A barrel lay in the water with a tag on it reading, "Dangerous Substance."
While the barrel likely isn't teasing the first reanimated animal on The Walking Dead, something which is well outside of the show's mythology (and quite possibly budget), it does seem to be building on some sort of mutated or radioactive walkers.
In Episode 8x02, King Ezekiel's group marched to a Savior outpost, encountering a walker with a unique appearance. Jerry quickly put it down with his axe but Ezekiel noticed some interesting burns and substances which had shaped this walker's appearance.
"What befell this creature?" Ezekiel asked. The question was never answered, outside of it being a tribute walker, based on Emil from Robocop -- a character whose death was thrust upon him by crashing into a radioactive container and later being hit by a car.
There is no storyline in The Walking Dead comics which uses substances to alter walkers but the AMC series tends to deviate from its source material from time to time to keep fans guessing. This substance may be part of a Savior plan to create a weapon against Rick's army, which may not even include walkers. It may be something used to create explosives or chemical weapons to be used in the All Out War story when Negan finally returns and will certainly be hungry for revenge after being attacked on his own doorstep.
Either way, the story of walkers affected by this "dangerous substance" has earned a mention already, giving theories regarding its importance plausibility. With walkers showing clear signs of being affected by the substance, humans will want to avoid contact with it. The question is whether or not anyone will weaponize the substance.