Yowl while pooping?

my cat has never done this, and up to this point he's a healthy 7 year old. scared the hell out of me to be honest, he yowled really loud this evening while pooping. it's late so vet care is not available until morning. any ideas ? 

thebaphomet said:

 
my cat has never done this, and up to this point he's a healthy 7 year old. scared the hell out of me to be honest, he yowled really loud this evening while pooping. it's late so vet care is not available until morning. any ideas ? 

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He sounds constipated or passing hard stools.  If he isn't passing stools at all then constipated, if he is then i would check consistency to see how firm they are.  If they are very firm then i would suspect constipation and would contact your vet.  The vet may suggest a small dose of metamucil in the diet, or mineral oil, but i would check the stool first and then call your vet.