@MrLovenstein
Average ant weights about 5 miligrams, so it can carry up to 0.25 grams.

Density of knife steel is about 7.75 g/cm^3, so an ant can carry a 0,323 mm^3 cube.

Let's make a knife out of this cube: we'll cut it in half and rearrange two pieces. We'll end up with a knife 0,646 mm long and 0,1615 mm wide with 0,323 mm high.

Now, the thinnest human skin can be found on the eyelids, which are 0,5 mm thick.
In other words, if you refuse to give him your wallet, an ant can left you without an eye even if you close it beforehand.