Valmiki Ramayana Ayodhya Kanda Sarga 28 Shloka 9
Original Shlokaसग्राहा स्सरितश्चैव पङ्कवत्यस्सु दुस्तराः। मत्तैरपि गजैर्नित्यमतो दुःखतरं वनम्।।2.28.9।।
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सग्राहाः with crocodiles, पङ्कवत्यः च filled with mud, सरितश्चैव rivers also, मत्तै: intoxicated, गजैरपि by elephants also, दुस्तराः difficult to cross, अतः therefore, वनम् the forest, नित्यम् always, दुःखतरम् more dangerous.
The rivers, infested with crocodiles and filled with mud are difficult to cross even for elephants in rut. Hence forest life is always extremely dangerous.