I have a pet hamster. I had previously stepped on some chocolate ice cream. As I was letting my hamster run around my room, she stopped and licked the spot of chocolate ice cream on my sock. Just one lick. I know chocolate is bad for hamsters. But will she be okay after licking that one lick?
Long to short: one drop of chocolate ice cream is not enough to harm your hamster.
The dangerous thing in chocolate is called "Theobromin". (look at this question for more detail: Does chocolate hurt hamsters?)
How much theobromin can a hamster eat without damage?
I have found an science article about dangerous dose of Theobromine for rats, mouse and hamsters.
The daily dose of theobromine which produced retrogressive changes in weight patterns and in the morphology of the thymus in both sexes and of the testes in males was approximately 250–300 mg/kg/day in mature rats and approximately 500 mg/kg/day in immature rats. Hamsters and mice were much more resistant to theobromine than were rats. A decrease in growth and in thymic weights occurred only at the highest dose levels of theobromine and testicular and thymic changes were completely absent in hamsters.
For your hamster it is important how much of this Theobromin was in the ice cream, and how much is the hamsters weight.
Hamsters weight are between 25g (1oz, dwarf hamster) and 200g (7oz, Syrian hamster). How much is yours?
The quote say: for mature rats 250mg/kg/day makes them ill. (They feed them 28 days every day this amount of theobromine), but for hamsters this was not a risk, they only get ill "on the highest dose".
250mg/kg/day means 0.25mg per g weigth.
So, following the article, a 25g hamster can eat 25 * 0.25 = 6,25mg of theobromin (daily for 28 days) without illness. A Syrian hamster can eat up to 50mg without risk.
How much ice cream has the hamster eaten?
This schools chemistry website says:
A gallon (3.8 liters) of ice cream must weigh at least 4.5 pounds, making the minimum density 0.54 gram per milliliter. Better brands have higher densities—up to 0.9 grams per milliliter.
One teaspoon of water approximately holds 5ml water. So one can assume that a drop of water is approximately one milliliter.
One drop of ice cream (one milliliter) then have maximal 0.9g = 900mg.
How much chocolate is in one drop of ice cream?
You can look at your ice cream box, maybe there stands something like "min. 15% real chocolate".
I found a receipt for chocolate ice cream with 300g dark chocolate in 1300g ice cream (this are under 24% of chocolate).
If we follow this, in a drop of 900mg ice cream are 300g/1300g*0.9g = 0.2077g real dark chocolate.
How much theobromin is in this amount of chocolate?
In the table of the above mentioned pet.SE question are 25g (1oz) of dark chocolate noticed with 130mg of theobromine. This is 5.2mg theobromine per one gram chocolate.
In one drop of ice cream is 0,2077g real chocolate, and with this 5.2mg/g * 0.2077g = 1.08mg of theobromine.
(Make the calculation from the other side: the most light weight adult hamster (25g) can eat 6,25mg theobromin: 6,25/1,08 = approximated 5,8 ice cream drops without getting ill)
So even with the most heavy (means highest quality) ice cream and a high amount of dark (!!)chocolate (over 23%) your hamster can not have enough theobromine with one drop of ice cream to get ill.