Just a couple questions, maybe they're stupid but hey....

Why do plecos 'blink'?

Last night after I cleaned the tank and all my plecos were crowded into the corner behind the heater, I was watching my rubbernose and Ancistrus sp. squabbling for more heater space and the Ancistrus sp. was actually flaring its gills at the rubbernose--I've never seen a pleco flare its gills before! I didn't know they could do that, has anyone else seen this?