Why a 3.5 kg cat's tongue won't pick up enough lactose
A cat's tongue holds about 0.014 ml per lick — that's roughly one drop from an eyedropper. Even if your Russian Blue licked the yogurt twice, she ingested less than a pea-sized amount. The lactose in this microscopic quantity gets broken down by yogurt's natural enzymes before her system needs to process it. Compare this to the milk in her saucer as a kitten, which had far more lactose concentration.
Watch for excessive lip-licking or a single loose stool tomorrow morning, but don't mistake her begging for more yogurt as a sign of distress. Cats love the fat content in dairy, which is why they'll act interested even when their bodies can't properly digest large amounts. The live cultures in yogurt may actually help her gut microbiome slightly.
When tiny amounts become a pattern
If this turns into daily yogurt theft from your breakfast bowl, the cumulative effect could lead to chronic soft stools. At 3.5 kg, your cat's digestive system is proportionally smaller than a human toddler's. What seems like 'just a taste' to you represents a notable percentage of her daily food intake when repeated.
Persistent dairy exposure can quietly disrupt the balance of her gut bacteria over weeks. While one incident is harmless, consider keeping yogurt pots covered if she's developing a habit. Cats are creatures of routine, and a new 'treat' can quickly become an expected entitlement in their minds.
The critical factor you already checked
You mentioned the yogurt was plain — this means no added sugars, fruits, or (most importantly) xylitol. Had this been flavored yogurt, even one lick could have been dangerous if it contained that particular sweetener. Xylitol triggers insulin release in cats at doses as small as 0.1 grams, which some yogurt brands use in 'sugar-free' varieties.
The fact that you saw the lick happen allows you to rule out other contaminants. Kitchen counters sometimes have onion powder or coffee grounds nearby, but a quick upward swipe wouldn't pick those up. Your cat's brief contact with a clean yogurt surface is the best-case scenario for accidental tasting.
How her body will process this tonight
Over the next 8 hours, the yogurt will move through her system without fanfare. Unlike dogs, cats lack significant salivary amylase, so digestion truly begins in her stomach. The proteins will break down first, then the minimal lactose will either absorb or pass through.
By morning, you likely won't find any evidence in her litter box — the quantity was too small to noticeably change her stool. If she curls up on your lap tonight, listen for normal digestive sounds. A completely silent or loudly gurgling stomach could indicate discomfort, but with this amount, her purrs will probably drown out any gut activity.
The full verdict, portion guidance and serving notes are collected on the Plain yogurt food facts page.