According to a study conducted by Royal Holloway, University of London, there's a science-y reason behind why we just can't keep our eyes open when we kiss (unless we're really not feeling it).
Psychologists Polly Dalton and Sandra Murphy found “tactile awareness depends on the level of perceptual load in a concurrent visual task".
In other words, the brain can't properly process another sensory stimulus while still concentrating on our visual stimuli.
The study, which was published in the Journal of Experimental Psychology: Human Perception and Performance, actually didn't involve testing people's responses to smooching (luckily, because that would have been super awkward for all involved).
According to The Independent, participants completed letter-searching tasks of varying levels of difficulty, while their tactile response was measured by a small vibration applied to one of their hands.Dalton and Murphy found that people were less responsive to the sensation while they focused on their visual tasks."These results could explain why we close our eyes when we want to focus attention on another sense," Dalton said."Shutting out the visual input leaves more mental resources to focus on other aspects of our experience."Sources: The Independent, Metro, The Telegraph