Can native spanish speakers trill their R with mouth/teeth in closed position? or its

Can native spanish speakers trill their R with mouth/teeth in closed position? or its
 

can native spanish speakers trill their R with mouth/teeth in closed position? or its impossible? thanks

Trilling requires air passing over the tongue. Therefore, if the mouth is totally closed shut, no trilling can occur. But even if teeth are clenched, air can still flow, so it is possible to trill an r with teeth closed.