Stanley brings home a pigeon that happened to be on the side of the road and doesn't tell Bill.
So like one night, Bills in the shower and the pigeon just casually slips in the shower with him.
All Stanley can hear in the distance is a high pitch scream and a weak "STANNNNNNN!"
Of course Stanley gets up from his chair--closing his favourite book and wonders over to the bathroom, which to where he sees Bill in the corner with a shower cap on--along with his arm outstretched holding on for dear life a backscrubber with a terrified, confused expression and the pigeon titling his head, cooing up at him.
Stanley stands there, fiddling with his fingers with a shy grin on his features, looking at them both and he goes " so, this is our son--Benjamin."