It is possible, if you catch enough unawares,
squeeze it tightly, and then, before it has time to
think, pop it on the scales
and take a reading.
Then you need to let it breathe:
release it carefully underwater, so it bubbles
upwards like a drowning hero
being measured for a suit.
Now you have its number; set it free, like a ringed
bird, to escape through itself, while you ponderously
calculate there's more of it in this room
than there is of you.