Why a spoonful won't harm a 4 kg dog
A tablespoon of plain sesame seeds contains no toxins for dogs, regardless of their small size. The main issue is mechanical: those tiny, hard seeds and their oil content might briefly irritate your Chihuahua's digestive tract. Given his weight, the volume is enough to notice but not enough to cause blockage or serious discomfort. Think of it like adding a bit of roughage to his usual diet—unexpected, but not dangerous.
Since it's been an hour, the seeds are already moving through his system. You'd have seen vomiting by now if they were going to cause immediate stomach upset. What's left is monitoring his stool for the next 12-24 hours. The seeds may appear whole in his poop, surrounded by slightly softer-than-usual stool. This is normal processing of unfamiliar fiber, not diarrhea unless it's watery or frequent.
When to expect (and not expect) signs
Between 6-12 hours post-eating is the window for any mild effects. A single episode of vomiting or one soft stool would be the upper limit of what's likely here. True diarrhea—multiple watery stools in a short time—would be surprising unless your dog has a pre-existing sensitivity to fatty foods. His small size means symptoms would show sooner than in a larger dog, but also resolve faster.
Don't mistake seed remnants for a problem. Sesame seeds often pass undigested, looking like tiny white specks in the stool. This is normal and doesn't mean nutrients weren't absorbed. What matters is your dog's behavior: if he's playful, drinking water, and not straining to poop, there's no need to intervene beyond skipping his next meal if his belly seems full.
The one risk that isn't about toxicity
For very small dogs, the main concern with any small, hard food is the slight chance of choking or temporary throat irritation. Since your dog ate these an hour ago without coughing or gagging, that risk has passed. The seeds are already in his stomach, where digestive acids will soften them. Unlike larger nuts or bones, sesame seeds are too tiny to cause physical obstruction in a dog's intestines.
Watch for excessive licking of lips or swallowing, which could suggest mild heartburn from the oils. This is rare with such a small amount but would pass within an hour or two. Offering ice cubes to lick can help soothe his throat if needed. Remember, the seeds themselves aren't causing this—it's just his system noticing an unusual texture and fat content.
Why you don't need to rush to the vet
Emergency vets see dogs for chocolate, grapes, and xylitol—not sesame seeds. No part of the seed contains dog toxins, and your Chihuahua's dose was well below any risky threshold. Calling the vet would likely get the same advice: watch and wait. The only exception would be if he has a known pancreatic condition that makes high-fat snacks risky, which isn't mentioned here.
Focus on hydration instead of worry. The extra fiber from the seeds may make your dog thirstier than usual. Keep his water bowl filled and expect him to drink a bit more over the next day. If he refuses water entirely or shows lethargy with vomiting, that's worth a call—but these would be extreme reactions to a benign snack. Most likely, this will be a non-event by tomorrow morning.
The full verdict, portion guidance and serving notes are collected on the Sesame seeds food facts page.