Eh, taik cair at 4 months tu normal sih, terutama if baby still on breastmilk or formula je, memang consistency dia macam tu. Tapi kalau suddenly jadi lebih cair, lebih frequent, atau ada signs lain macam demam or rash, better check with your paediatrician to make sure okay lang, sebab at this age boleh jadi sensitivity or something yang kena address. A few of my mum friends also noticed their babies jadi loose stools when they're introducing solids or if the weather is hot, so it's not always susu yang tak sesuai, but honestly, paediatrician is the best person to confirm whether it's normal or if formula adjustment is needed.