I think I'll make this a new feature, since all kinds of interesting things pop up in my Google Scholar searches. Here's one:
Urine makes the difference : chemical communication in fighting crayfish made visible
Thomas Breithaupt and Petra Eger
In this study, they were interested in chemical communication between crayfish who were fighting with each other. So they blindfolded the crayfish, and then used fluorescent dye to see the urine. Evidently, they fan the urine toward each other using their gills or maxillipeds.
Here's part of the abstract:
Aggressive behaviour is effective in intimidating blindfolded opponents only in conjunction with urine release: receivers decrease offensive behaviour and increase defensive behaviour. Aggressive behaviour alone does not intimidate opponents. The loser of a recent fight is deterred equally well by a familiar and an unfamiliar opponent. Hence, in crayfish, individual recognition of the urine scent of a dominant individual does not appear to be significant for the maintenance of dominance hierarchies. Our results suggest that urine contains information about the fighting ability and/or aggressiveness of the signaller. The chemical signals thus far unidentified appear to be important in determining the outcome of a fight.
Breithaupt T, Eger P. 2002. Urine makes the difference : chemical communication in fighting crayfish made visible. J Exper Biol 205:1221-1231. Abstract