The soldiers at Bukit Bunga (Flower Hill) in Kelantan were dipping their toes in the waters of the river that forms the border at that point between Malaysia and Thailand.
By Jonathan Kent
BBC correspondent in Bukit Bunga, Malaysia
Fallout from the fighting in the Thai Muslim south could spread
One runs up the bank below me to help a young boy, no more than 10 years old, lift his bicycle over the barbed wire.
The boy pushes his bike through the shallow water over a sandbank, through another stream and runs to see his friends on the other side, where Thai flags flutter.
There is no bridge here and most cross by boat or simply wade through the river.
Borders probably do not mean much when you are 10 years old.
They do not seem to mean much to most people along the frontier here.
The current arrangement dates to the early 20th Century when Britain, the colonial power in the south of the Malay peninsula, struck a deal with Thailand.
Britain kept the states of Kelantan, Perlis, Kedah and Terengganu; Thailand retained control of its five southernmost provinces, which once formed the semi-autonomous Sultanate of Pattani.
What all these areas have in common is that their populations are predominantly ethnic Malay and Muslim.
Many Kelantanese have businesses in Thailand, many have Malaysian and Thai passports, though it is illegal to do so, and some even have wives on both sides of the border.
Many Malay Thais send their children to Malay language schools in Malaysia.
Locals are just waived through. There are no document checks - a familiar face is passport enough.
But since Wednesday, that relaxed attitude has stiffened.
The soldiers at Bukit Bunga said reinforcements had arrived.
"They sent an armoured car," one told me.
And had they stepped up patrols?
Recent zones of unrest in southern Thailand border Malaysia
"Twenty-four hours, round the clock," he said.
The reason: both Malaysia and Thailand suspect that those involved in the violence in southern Thailand may try to cross into Malaysia.
"We are worried most about the possibility of Thai nationals crossing over to our border to seek refuge or those hunted and suspected of having carried out the violence," the Malaysian Prime Minister Abdullah Badawi said on Thursday.
"That will be a threat to us also."
Malaysia does not normally comment on its neighbours' affairs but this time it appears the government could not keep silent.
The soldiers are worried too and not just about the Muslim separatists some blame for the violence.
They are worried just how the news that more than 30 people had been gunned down by Thai security forces inside a mosque will go down not so much here as north of the border.
"It's bad," they said.
Twenty kilometres further up the frontier at Rantau Panjang the police are present in numbers, with camouflage and sub-machine guns .
Support for the Pas party leader is strong in Kelantan
Kelantan is enjoying its first proper rain for three months and the police have pulled up their chairs under a shelter so they can keep an eye on comings and goings.
Like most in Malaysia they are built for comfort not speed.
"You know what?" one asked me. "Those bodies on TV, the guys lying in the street who are supposed to have attacked the Thai police? Where was the blood?
"First thing I'd tell you if I was at that crime scene - they were shot somewhere else and moved there. If they'd been shot there, there would be blood everywhere."
The official Thai government line about bandits high on drugs and cough syrup does not cut much ice in Kelantan; instead conspiracy theories abound.
And while this side of the border seems a world away from the troubles in Thailand there is concern here that those troubles won't go away fast.
Strangely though, the group I had expected to be the most vocal is one of the quietest.
Muslims in Malaysia's north look over the border with concern
Since last month's general election Kelantan is the only state controlled by Malaysia's conservative Islamist party, Pas.
But at the state government offices, no one wants to speak.
The state's economic development minister, Husam Musa, normally eloquent and forthcoming, is too busy to see me.
The Chief Minister's political secretary says it is only for Malaysia's Foreign Minister to comment on international matters - which is odd, since Pas has organised heaven only knows how many anti-US demonstrations over Afghanistan and Iraq.
Pas is caught between a proverbial rock and a hard place.
If they condemn the storming of the mosque they are painted by their opponents as supporting militants.
If they don't, their supporters ask why they are not standing up for oppressed Muslim brothers in Thailand.
The violence there is already a hot potato in Malaysian politics.
Malaysia remains a stable Muslim island in a troubled sea.
There is violence in Aceh and Ambon in Indonesia, the Southern Philippines island of Mindanao, Muslim Rohingyas still flee Burma and the militant groups Jemaah Islamiah, Abu Sayyaf and the rest keep recruiting.
The last thing south-east Asia needed now was for non-Muslim troops to storm a mosque and wreak havoc, analysts say.
Where it goes from here, no one knows.