Why would you eat carpet?

S.'s dog ate large portions of carpet around the house on Saturday. I tried to take him for a walk yesterday, he sat down in an almost meditative position on the neighbors lawn. I asked him if he was too hot and wanted to go home and he responded by barfing up part of the downstairs carpet. When he finished he said he wanted to go back home, we walked back to the front yard. He sampled some grass but not the good barf inducing kind so I directed him to where it was growing. He grazed and after a spell vomited up more downstairs carpet, then a little upstairs carpet too. Six generous clumps. Some I had to extract from his throat as they were stuck half way. Delightful on a 90 degree day.