At five months old, babies are becoming more aware of the world around them, and their developing social and motor skills play a big role in what makes them laugh. Here's what may be going on:

Activities that can make your 5-month-old baby laugh aloud:
1. **Peek-a-boo**: At this age, babies are starting to understand object permanence (the idea that something exists even when they can't see it). Playing peek-a-boo can be delightful because they are learning that you’ll come back when you hide and reappear. The surprise element can evoke laughter.

2. **Funny Faces and Sounds**: Babies are very responsive to exaggerated facial expressions and silly noises. Smiling, making different sounds, or changing the pitch of your voice can easily make them laugh.

3. **Tickling**: Gentle tickling or touching their belly, feet, or underarms can lead to giggles as they become more sensitive to touch. However, be mindful of their response; some babies may get overstimulated by too much tickling.

4. **Playing with Toys**: Babies at this stage love exploring textures and sounds. A soft toy that crinkles, a toy that squeaks, or a rattle can capture their attention and make them laugh as they discover new sounds and sensations.

5. **Swinging and Bouncing**: Movements like gentle bouncing on your lap or being swung in the air safely can create fun and laughter. Babies enjoy the sensation of motion, and it can make them giggle out loud.

6. **Imitating Their Noises**: When you mimic the sounds they make, babies often find it funny. It’s part of early communication development and can evoke a laugh when they recognize that you’re copying them.

How Much Can a 5-Month-Old Understand?
At this stage, your baby is becoming more social and starting to understand emotions through facial expressions and voice tones. Here’s what they’re likely to understand:
- **Tone of Voice**: They can recognize when you’re happy or excited by the tone of your voice. A playful, upbeat tone often leads to laughter, as they sense joy from your sounds and actions.
- **Facial Expressions**: Babies this age are very in tune with faces and can detect emotions through expressions. A smiling or exaggerated expression is highly engaging for them, and when combined with a fun action (like peek-a-boo), it can lead to laughter.
- **Cause and Effect**: While they’re just beginning to grasp the concept of cause and effect, they can still find it funny when they make a noise and you respond or when a toy makes a noise after they touch it.

At this point, the baby is not fully understanding jokes or humor the way older kids or adults do, but they are starting to connect emotions with actions. What makes them laugh is usually tied to surprise, joy, and new sensory experiences.