Caffeine (and theobromine relatives) overstimulate heart and nervous system. Grounds, beans and tea bags are concentrated — a knocked-over cup is rarely a crisis, a bag of grounds is.
Same, with an even smaller margin.
Methylxanthine stimulants; dose = concentration × body weight.
Restlessness, panting, tremors, racing heart.
ASPCA Animal Poison Control: (888) 426-4435 · Pet Poison Helpline: (855) 764-7661 — 24/7, a fee may apply. Your own vet first when reachable.