Why a 4 kg cat reacts differently to chocolate than dogs
Cats lack the liver enzymes to efficiently process theobromine, chocolate's main toxin. While dogs often vomit first, cats tend to show neurological signs like trembling or twitching — exactly what you're seeing now at 20 minutes post-ingestion. That single bite likely delivered enough stimulants to make her jittery without reaching dangerous levels, but her small size means even mild symptoms deserve attention.
Watch for muscle stiffness or exaggerated reflexes — these suggest theobromine is affecting her nervous system more severely. Unlike dogs who pant or drool, cats may simply sit very still while their legs tremble slightly. If she tries to jump and misses, or her pupils look dilated, the dose was likely higher than you estimated.
Timeline of risks after a chocolate bite this small
Peak effects hit between 6-12 hours in cats, so her current shakiness may intensify slightly before improving. The first two hours are critical for observing whether she'll vomit naturally (which removes some toxin). Since chocolate moves slowly through feline digestion, symptoms can persist for up to 24 hours — though with just one bite, they should remain mild.
Set up a quiet, dim space with her bed and water bowl nearby. Stress worsens trembling, so avoid sudden movements or loud noises. If by hour three her shaking progresses to full-body tremors or she refuses water, the dose may be affecting her more than initially thought.
Comparing this nibble to dangerous chocolate amounts
A 4 kg cat would need to eat about 10 grams of dark chocolate (or 30 grams of milk chocolate) to risk severe poisoning. Your "small bite" probably contained far less — likely under 2 grams unless it was baker's chocolate. The shakiness alone doesn't indicate toxicity yet, but confirms her body is reacting to the stimulants.
Check her gums: if they're pale or feel tacky instead of slick, circulation issues are developing. Normal pink gums mean her cardiovascular system is handling the load. Time her breathing for 15 seconds and multiply by four — anything over 40 breaths per minute at rest suggests discomfort.
When shaky becomes an emergency
Upgrade to immediate vet care if her trembling spreads to the jaw (look for "chewing gum" motions) or she vocalizes uncomfortably. These suggest muscle spasms rather than mild stimulation. Similarly, if she presses her head against walls or walks in circles, neurological involvement has crossed into dangerous territory.
For now, note whether she can still groom herself or land jumps normally — coordinated movement means the dose is manageable. Keep other pets away; some cats become defensively aggressive when feeling neurologically "off." If midnight passes without worsening, the worst has likely passed.
The step-by-step response, from the first minute to the vet visit, is in our Shaking or Trembling emergency guide.