Why 4kg matters with two teaspoons of seeds
A 4kg cat consuming two teaspoons of loose poppy seeds is at the low end of concerning quantities. While this exceeds casual exposure (like licking a bagel), it's still unlikely to deliver enough opiates to cause severe sedation. The main variable is whether your cat chewed the seeds—whole seeds may pass through with minimal absorption, while crushed ones release slightly more compounds.
Your kitten's avoidance was fortunate but doesn't change the approach for your other cat. Focus on the exposed pet: check for any immediate regurgitation (some cats vomit simply from eating unfamiliar dry textures) and ensure fresh water is available to help flush their system.
Timing clues in the 20-minute exposure window
The 20-minute unsupervised access suggests your cat didn't gorge continuously—they likely ate intermittently, which reduces the chance of overwhelming their system. Cats rarely binge on dry seeds unless extremely hungry or attracted by other flavors (like oil residue on the bag).
If ingestion occurred less than an hour ago, you might notice your cat licking lips or showing mild disinterest in food—normal reactions to an unusual snack. True toxicity signs (staggering, slow breathing) would typically appear within 2-4 hours if they're going to manifest at all. By contrast, the kitten's zero exposure means no observation is needed for them.
Weight differences between your two cats
Your 4kg adult has slightly more metabolic capacity to process the seeds than a smaller cat would, though the 3kg kitten's avoidance makes this moot. Never assume weight alone determines safety—a tiny amount can affect some cats disproportionately based on individual sensitivity.
Had the kitten eaten even half the amount, their smaller size would elevate concern, especially since young cats are more vulnerable to central nervous system depressants. For your adult cat, the dose per kilogram remains subclinical unless they exhibit the rare sensitivity to trace opiates.
When to escalate beyond watching
Monitoring is sufficient unless your cat displays specific red flags: inability to stand steadily, pupils that don't constrict in light, or breathing slower than 20 breaths per minute at rest. These would indicate atypical opioid effects requiring urgent care.
More probable but less urgent signs include mild drowsiness or reduced playfulness for a day. If these persist beyond 24 hours or worsen, consult your vet. Otherwise, the seeds should pass through without incident—just ensure your cat stays hydrated and eats their normal meals to help move the material through their gut.
The full verdict, portion guidance and serving notes are collected on the Poppy seeds food facts page.