Fun with foil

Okay I know in the day we could make a pipe out of a cardboard T.P. tube and some foil or use foil to burn a little Hash Oil but again I have a mystery.Last night I cooked some Angel Hair pasta and put the left over pasta in an alum bowl and covered it with foil.About an hour ago I went to nuke some and what do I see but tiny little holes in the foil!Now what in the hey could cause that?.I cooked the pasta in salted water and I did put the bowl on top of a closed pot of tomatoe sauce but no way it could have leaked through.