My girlfriend says her lips get numb after giving me head any particular reason this happens?

She is putting a lot of pressure on her lips; there is a lot of friction. It is only normal for her lips to go numb. My girlfriend says her lips get numb after giving me head any particular reason this happens?
she is probably covering her teeth with her lips so she doesn't accidentaly nick you, the pressure her teeth are putting on her lips can cause them to go numb for a little whileMy girlfriend says her lips get numb after giving me head any particular reason this happens?
she's covering her teeth with her lip
ya

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