You should pay close attention to their body movement.
However, below are some signs that guarantee a person is enjoying sex. So make sure you listen and pick up on any signs they may not mean it.
We all make different noises when we are having sex. Some people will sigh, giggle, and scream. However, others will have sex in utter silence, but are having the time of their lives.
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People make different facial expressions when they’re they experiencing a lot of pleasure. Some people even look as though they’re in pain. Everyone is unique and if you know your partner well, you’ll probably recognize the facial expressions they pull when they’re enjoying themselves.
So if they’re flirting with you, touching you and kissing you when you’re not having sex, this is a sign they’re happy with your sex life. The touchy-feeling with you outside of the bedroom is a sign they're happy with your relationship as a whole, too.
If somebody is pulling you towards them, or pulling themselves towards you, that’s a clue they’re having fun. "They’re likely to be saying, 'give me more - I’m enjoying it'. However, they could also be trying to switch angles or positions so the sex is more pleasurable for them.