T-Rex arm and hand flapping are both ways of making your senses happy, which is a common behavior among autistic people. Making your senses happy is any repeated or rhythmic behavior that makes one or more of your senses feel good, such as rocking, spinning, humming, or tapping. T-Rex arm and hand flapping are both ways of making your senses happy and they both involve the arms and hands, but they have different movements and purposes. The T-Rex arm is holding the arms close to the body with the elbows bent, while hand flapping is moving the hands fast up and down or side to side. T-Rex arm even makes you feel safe or comfortable, while hand flapping makes you show excitement or joy.