On, out, up, in- they're all pretty much the same.
Hubs: I let the cats out.
DON'T LET THE CATS OUT, THEY EAT ALL THE CAT FOOD AT THE NEIGHBOR'S HOUSE!
Hubs: I let the cats UP. (they stay in basement playroom at night because they run like crazy at 2 am and wake everyone up.)
See the difference? Even the littlest words have power... Choose your words carefully....