1.https://pethelpful.com/dogs/-Why-Dogs-Sometimes-Lick-their-Lips-Excessively
2.https://www.acvs.org/small-animal/salivary-mucocele
3.https://www.petmd.com/dog/emergency/common-emergencies/e_dg_bloating
4.https://www.thespruce.com/dog-body-language-lip-licking-1118243
5.https://academicworks.cuny.edu/cgi/viewcontent.cgi?article=1025&context=hc_sas_etds
6.http://www.petmd.com/dog/general-health/evr_dg_acral_lick_granuloma_a_dermatology_nightmare
7.http://www.goodhousekeeping.com/life/pets/news/a39242/dog-bacteria-infection/
8.https://www.companionanimalpsychology.com/2017/09/do-dogs-use-body-language-to-calm-us.html