My pronunciation "LIE SEE" obviously didn't help but I did get the answer, albeit making no sense of it!
I'm baffled partly by 15 Across - "Animals swallowing have too many units (7)". There would appear to be two options "VOLUMES" or "MODULES". Both have small animals but where do we get "swallowing" from "UM" or "DU"? I can see that "UM" can indicate a hesitation but surely "swallowing" would best be indicated by "GULP"?
As is so often the case I'm sure it's blatantly obvious! Perhaps Roman numerals - 500 U or U 1000?
Regards to all.