Ling was convinced that Greed was setting him up for his own amusement.
Of course, if Ling were honest, he enjoyed seeing the homunculus as the butt of a joke now and again. Ling certainly would be the first to smirk and say, "I told you so," when Greed's schemes went sour ... but that didn't mean he enjoyed the reverse. Thinking back on it, he'd never had to deal with being laughed at like this - or at all - until he'd come to Amestris, which probably played a part in his current displeasure. Amestris was a very fascinating country, if nothing else.
Greed laughed quietly in the corner of their mind, and once again Ling couldn't help but feel this had been planned.
"If you think relinquishing control like this will stop me from fighting you, you're wrong, Greed."
The homunculus barked out hard, quick laugh. "I wanted a break and some entertainment. Don't go reading into things that aren't there, kid."
When Ling said nothing in return, Greed laughed again. Ling ignored him - and sorely missed Xingese closures. He had to figure out how to get these pants unstuck and closed back up before the others came looking for him again. Ed always got upset when they "took too long to piss."