He means those times when he has to shoot short, chubby, hairy critters... Like hamsters, Bill Oddies and guinea pigs. It's a filter which works a bit like an anamorpohic by making things seem thinner and taller. It's used a lot in films, Jeremy Irons is, in fact, only five foot tall and quite fat but with the "thin filter" he looks tall and thin. Julia Roberts, in real life, looks like a bowling-ball with legs.

Either that or the "nightshot" mode.