Marley shows the others the entrance to the cave. "This way maybe?" he suggests.

DM: going to assume y'all go for it.

Everyone give me a dex or str check.

Yeah let’s do this. Str: 14

(Just to confirm, you mean 'Check' and NOT 'Save'. I ask since I would add my Prof Bonus)

STR Check: 5

Yep str check

Marley DEX check: 16

dex: 15

As expected the two more slinder members of the party slip right through. Sam and Crunchface get stuck and have to back out. 

You both study the hole for a moment and determine you need to go in feet first and have the others pull you through.

Roll again with advantage 

19

Sam STR 15

On the second attempt you both squeeze your way through.

You find your self in a natural tunnel. It extends in both directions 30 ft before turning a corner into darkness.

Which way do y'all go.

(Can we tell which way the rat went?  Or does either side have more droppings?)

Sam STR (adv) 7

Give me a survival check

Marley Survival: 14

(been sick with the flu starting to recover)

With a 15 you see a clear pattern starting to form traveling towards the left. From what you can tell there are possibly hundreds of not thousands of rats ahead

Marley stands from where he knelt to closely examine the cavern floor and shakes his head with a scowl as he looks to the others. "There are a LOT of rats ahead my friends, maybe many hundreds or more..."  He scratches at his ear as he frowns thoughtfully, then wonders out loud. "Do we have what we need to deal with this?"

"We could use fire. Anyone got any oil we could throw?"

(Wishing I’d taken some AoE spells now)

Crunch shakes his head. “No.”

Marley also shakes his head.  "We could head back up and get some, but... there is the one that got away."