**Core Concept**
LINSEED (or *Ricinus communis*) contains ricin, a potent toxin, but the poisoning associated with its ingestion in cattle is not due to a classic alkaloid like aconite or atropine. However, linseed seeds, when processed or consumed in large quantities, can release hydrogen cyanide (HCN), a volatile hydrocyanic acid, which acts as a rapid-acting cyanide poison.

**Why the Correct Answer is Right**
Hydrocyanic acid (HCN) is released during the breakdown of linseed oil or when linseed is fermented in the rumen. In cattle, ingestion of linseed leads to cyanide toxicity due to the presence of cyanogenic glycosides in the plant. These compounds are hydrolyzed by gut enzymes, releasing hydrogen cyanide, which inhibits cytochrome c oxidase in mitochondria, leading to cellular hypoxia and rapid death. This is a well-documented case of cyanide poisoning in ruminants.

**Why Each Wrong Option is Incorrect**
Option A: Aconite poisoning is due to *aconitine* from *Aconitum* species, not linseed. Aconite is not found in linseed plants.
Option B: Atropine is a muscarinic antagonist derived from *Atropa belladonna*, unrelated to linseed.
Option C: Pilocarpine is a parasympathetic agonist from *Pilocarpus* species, not present in linseed.

**Clinical Pearl / High-Yield Fact**
Always remember: *LINSEED causes hydrocyanic acid poisoning in cattle due to cyanogenic glycosides*, not alkaloids. This is a classic example of plant-induced cyanide toxicity in ruminants—common in pastoral areas where linseed is used as feed.

✓ Correct Answer: D. Hydrocyanic acid